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Magnetic rocks again
Posted by Anonymous User
Anonymous User May 29, 2012 11:49PMI asked in an earlier post if anyone could show me images of weak magnets sticking to basaltic andesite or other rocks other than loadstone, as ive found tons of it, yet i still can't find images myself and it seems forum members have not come across simmiler rocks?
Anonymous User June 03, 2012 12:12AMAnd more this piece i admit does puzzle me ! but the thing it does remind me of is the sands of the beaches of some of the med isles sands that are full of magnetite !
Edited 1 time(s). Last edit at 06/03/2012 12:18AM by Heath Barnes.
Ralph Bottrill June 03, 2012 02:21AMHeath, you really need a polished thin section for starters, to see if it really is a basaltic andesite with magnetite, or something else; you really cannot identify a rock like that without microscopic studies, it could be a hornfelsed sediment or a dozen different things.
Dan R. Lynch June 03, 2012 06:24AMI've seen the hullabaloo over this topic in other threads, and I'm not sure I want to add to it. But I agree with Ralph that it isn't clear that the rocks in your photos are basalt or andesite. Some closer observation is certainly necessary.
I will add that on Minnesota's Lake Superior shoreline, a strong magnet will easily pick up pebbles of basalt that have a high enough magnetite content. But the pebbles are small and light weight, so it's not surprising and is nothing to get excited about. They're pretty weakly magnetic and a common refrigerator magnet won't cut it, either. A strong neodymium rare-earth magnet will grab up to thumbnail-sized basalt stones, but I've never come across a whole boulder that a magnet would stick to.
Edited 1 time(s). Last edit at 06/03/2012 06:41AM by Dan R. Lynch.
Anonymous User June 03, 2012 02:08PMDan and Ralph the missunderstanding may well be my falt in the way ive posted, the pictures including the new ones showing the cobble fashiond from the basaltic andesite mined from a local outcrop of the Cleveland dyke, And the larger boulders that i have found and arranged for others to view and test whenever needed.
The following was sent to me by a geologist from a local University. Chemecal annalysses of iron content in whin sill compared with Cleveland dyke.
Great Whin sill( Harrison 1968) : Fe 2 0 3=3.25%
Cleveland dyke, Bolam ( Holmes Harwood ), min magazine 1929 : Fe2 =3.12%
Fe0 = 6.60 %
It was thought that stone from the whin sill had roughly
24% more iron than stone from the Cleveland dyke
I believe the fact i can attatch a fridge magnet to each piece of basaltic andesite belonging origionally from the clevelland dyke, shows it at this location has a much higher iron content than previously thought. Also the gravel beds i am currently excavating are crammed with what i believe to be the same material all of which is easily attracted to the same fridge magnet.
Anonymous User June 03, 2012 02:25PMHeath Barnes Wrote:
> Sorry forgot the arranged basaltic andesite
> boulders all easilly atract a fridge magnet.
Also the first pic shows a piece of the origional mined dyke stone at the entrance to the quarry plantation note the magnets attatched.
Roger Curry June 03, 2012 03:23PMHi Heath,
I'm a factory worker with no qualifications in geology. But, like you, I have a strong interest in the natural world. I just live down the road from Middlesborough. I've been facinated by your field work and finds. I think perhaps there has been a few problems between yourself and folk trying to help here on Mindat. It's the nature of the type of communication - that is, by text- that misunderstandings can easily occur.
I'd really like to meet you (possibly over a pint?), and learn more of what you're doing and finding. I think a face to face discussion about this topic could clear up a few points about the subject, and I'll learn from you! You have much more knowledge about what's going on there than anyone else. Sometimes it's useful to talk to someone else, to get focussed on the direction of interest.
I've found a book online which mentions Stainton quarry-
"...earthy aspect among of basalt in patches or irregular veins. A vein of wacke three or four feet wide occurs in Stainton quarry where the authors also observed some of the most interesting varieties of the basalt."
This is from the chapter "The Basaltic Dyke" in "A geological survey of the Yorkshire coast" by George Young in 1828. The basalt making up the dyke certainly seems to be chokker with iron from this description -
"The rock is not uniform in its qualities Most of it exhibits the recent fracture a rough granular surface of a dark blackish colour with a number of shining specks sometimes of the same colour sometimes darker and sometimes lighter Very often the stone quite black with scarcely any tinge of blue The shining crystals frequently oblong and thin like those in the blue limestone We not perceived among them any olivine or augite The rock is remarkably hard and supplies excellent materials for making roads for purpose it is quarried in several places It seems to owe a great of its hardness to the quantity of iron contained in it from whence the blocks derive their rusty coating Some varieties of the stone appear like a mixture of clay and iron and abound so much with the latter that their recent fractures often exhibit a grey iron colour soon acquires a rusty hue on being exposed to the weather specimens are not so compact as the black or blue basalt but abound with veins or crevices many of which are filled or lined calc spar while others are empty Similar cavities sometimes in the black basalt containing crystals of calc spar some of are of a dull white colour while others are highly transparent beautiful having laminated shining surfaces Along with such crystals we find in some of the crevices or small veins a soft substance consisting of very minute jet black grains slightly adhering to other and having a glimmering lustre When a portion of this substance is subjected to a red heat the black colour is discharged it acquires a yellow brassy or pyritous aspect the grains having metallic lustre and adhering more closely together During process there is no appearance of ignition The substance is evidently a metallic oxide and is probably the black oxide of iron with a slight mixture of sulphur Rhomboidal crystals of calc spar are imbedded in it."
Section 2 of the book concerns the organic remains in the areas covered. I know very little about this but I'm sure you'll find it of interest.
I have no further information nor expertese to offer on your geological deposits and fossils. What I can offer is an attempt to identify any minerals, and a general natter about North East geology and your finds, should you wish to meet up.
Keep up the good work,
Anonymous User June 03, 2012 09:00PMFirstly Rog thanks for the piece you found on the dyke at stainton ive never come across it before, and ile be getting a copy of the book. and yes mate we will have to meet up maybee i could show you round some of my excavations at stainton and yes a couple of pints after!
As for the missunderstandings so far this happens as you say but we will never descover new things by trying to pleasing everybody, let me know if you fancy a look around up here, ime off work till next monday now. All the best Heath.
Anonymous User June 04, 2012 10:33PMI would have thought i may have had some members who openly stated that i had indeed not discovered that this part of the basaltic andesite Cleveland dyke was indeed highly magnetic compared to anything found before, would have wanted to comment further ?
Tim Jokela Jr June 05, 2012 02:55AMWhat the hell is this all about? You found some magnetic rocks?
Are you a creationite trying to make some sort of point, or what?
Do you know what this website is about? (It's for mineral collectors.)
Do you think this is the proper place to make hundreds of posts about some magnetic rock you found?
I'd understand your excitement if you unearthed a T-Rex skull with a hominid femur 'twixt his fearsome teeth... but, what are you on about???
Roger Curry June 05, 2012 01:33PMMr. Jokela,
Chill out dude, you needn't read Heath's posts. I am very interested in his work and I'm looking forward to examining some of his finds. He's seeking knowledge on this forum and, although he can be a little excitable when folk appear condescending, none of his posts (or those from people responding) contain the unpleasant arrogance your post clearly shows.
Anonymous User June 05, 2012 01:56PMMr Jokela i havn't mentioned much about the fossil content of the gravel beds becouse as you rightly say its a mineral forum, but i can assure you the age of a lot of the well preserved fossils to be found in abundance in this gravel bed are a lot older than Cretaceous and Jurassic. The bed rock under the gravel bed at the dyke location is Triassic, so i don't think even if i reached the bedrock ide be finding many T rex fossils sorry about that.
All the very best Heath.
Mark J. Sigouin June 05, 2012 06:52PMBasalt or andesite, no matter, both can possess zones locally enriched in magnetite which will attract magnets. Iron content itself does not automatically produce magnetism or the ability of magnets to attach. The richest hematite iron ore often has a huge percentage of its molecular weigh as iron, yet is never magnetic because the atoms of iron have to lay in particular areas of the crystal lattice in order to produce magnetism or be attracted by a magnet. (By the way, those magnetic hematite beads found in the kiddie section are artificial and not made of hematite at all.) Magnetic properties have much more to do with the location and spin of the electrons in the molecule than simply iron content.
I suggest you read the article about magnetism on wikipedia. It will initially look intimidating, but pretty quickly you will get the idea as to how magnetism really works.
Your volcanic rock may look uniform, but as a previous commentor stated, microscopically you would probably find it isn't. You might find different areas in the outcrop where olivine, or the feldspar will wax and wane in concentration, Places where the magnetite concentration rises and falls, but over all it is basalt or andesite. In nature, it is rare that a totally uniform solid is ever created.
Anonymous User June 05, 2012 10:01PMThanks for that Mark and it sounds like you have read some interesting stuff, but please understand i am not alone here ive had examples examined by experts, and understand what the magnetic properties of basaltic rocks but i say yet again there are no records that i know of were any person professional or amature has managed to attatch a fridge magnet to any samples or as i have make small samples of basaltic andesite jump on to the same magnet, also this material from the basatic andesite dyke at stainton reacts in different way to the possative and negative, please understand i do not pretend to understand fully what ive come across only that it does not add up.
In a hope to make people understand that ime not trying to be something ime not, as my blog records i started off on this becouse ide found a carved bone artifact 5 years ago that the local archaeologists could not determin its age or possible use, i made a prommis to my daughters ide find out what it was used for and from what time in human history it was made, ime still digging !
Anonymous User June 06, 2012 08:53PMMark i have previosely red articals on how magnets work and indeed how its possible to make one, and found it both hard work yet fascinating. this dyke thing i stumbled upon i knew little nore cared little about geology at the time but found i could not egnore it, and so far there is no satesfactory explanation, i qoute a geologist who has visited this section of dyke with me, who describes it as a phenomenon.
Here is a pic took today showing small kids magnets stuck to a large piece of basaltic andesite left over from the quarry works, that ended in around 1928. Regards Heath.
Becky Coulson June 06, 2012 09:18PMHeath, I found an excellent thesis (2005) including magnetism in the Cleveland Dyke. I hope this link works.
I think you will find it fascinating - especially the high magnetite content. Becky
Edited 2 time(s). Last edit at 06/06/2012 09:52PM by Becky Coulson.
Anonymous User June 06, 2012 11:37PMSorry Becky the link never worked but please believe me i can not make most work either! but it sounds very interesting ive been informed of a report maybee the same where it is reported this section of dyke is rich in a certain rare magnetite, sorry withought trawling my blog which is a pain i can not remember the name of, hopefully some kind member will show us both an easy way to add these links! :-)
Becky Coulson June 07, 2012 07:02AMHeath, Type this into your Google search: "magnetic investigations of igneous intrusions in teesdale" .
The first thing that appeared was a link to the thesis. Please give it a while to load - it took at least 30 seconds for the thesis to appear on my blank screen. Good luck! Becky
PS - The full thesis is in PDF format, and you will need an Adobe Reader to see it. The Adobe Reader is a free download.
Edited 1 time(s). Last edit at 06/07/2012 07:27AM by Becky Coulson.
Roger Curry June 07, 2012 12:05PMHi Becky,
Nice find! Only had time to briefly look through it, but it certainly shows that what Heath has found is of such interest that it has been studied in great detail with proton magnetometers and thin sections. Equipment wise, a far cry from the compass, fridge magnet and big hammer I hope to use tomorrow!
Heath, it just shows you mate, you've seen something unusual enough for a guy to study for a couple of years for his PhD! I'm fascinated in both the magnetic dyke and your fossil finds, will PM later today about travel.
Edited 1 time(s). Last edit at 06/07/2012 12:07PM by Roger Curry.
Norman King June 07, 2012 04:19PMOf course, I have not quit following this thread. Roger, the text that you cited written by George Young in 1828 reports no indication of augite in the sample he examined. It turns out the primary rock the Cleveland dyke swarm is a basalt (or diabase) rich in clinopyroxene (such as augite) and Ca-plagioclase. But Young’s reference to the rock appearing to be a mixture of iron and clay suggests a sedimentary ironstone. He also mentioned that calcite is prominent, as well as the presence of jet–a kind of coaly material.
The WNW-trending dykes are well-known in the area. In places their intrusion has created contact metamorphic zones resembling skarns formed where igneous rocks have intruded carbonate sedimentary rocks, producing in this area, among other things the calcium-rich silicate wollastonite.
Becky alerted us to the master’s thesis by Elijah Mwandoe. Mwandoe also refers to the Whin sill that was intruded during the Carboniferous, in contrast to the Cleveland dyke swarm that was intruded during the Paleocene. The only reference Mwandoe makes to these rocks being attracted by a magnet is to the Whin sill (which IS so attacted, and does crop out in a few places in the area). As Mwandoe himself stated, his study was inspired by presence of niccolite and other nickel-bearing minerals associated with magnetite in the Harwood Valley area of northern Teesdale, as well as by a previously-known magnetic anomaly, to see if those are related.
This “magnetic anomaly,” however, has nothing to do with magnets being attracted by the intrusive igneous rocks in question, hence to the presence of magnetite. The Jurassic oolitic ironstones in this area are rich in magnetite–unusual for oolitic ironstones. The mechanism by which berthierine ooids were partially replaced by magnetite ooids still seems to be a matter of debate. But the “magnetic anomalies” refers to a departure from the regional values of magnetism present in the upper part of the crust throughout this region. Such anomalies, detected by surface remote sensing, often tell us much about what is in the subsurface in areas where there has been little or no deep drilling for samples and direct measurements.
Roger Curry June 07, 2012 04:49PMHi Norman,
Re. "His reports of the rock being highly magnetic also did not seem to me to represent any plausible igneous rock of which I am aware." from thread "highly magnetic dykes--NOT!"
I'll hammer a lump off tomorrow.
Edited 1 time(s). Last edit at 06/07/2012 05:01PM by Roger Curry.
Norman King June 07, 2012 06:19PMRoger,
That is exactly what needs to be done. Well, one of the things--field relationships have to be determined also. I mean MUST BE determined! (or we'll never get this figured out).
Can you send me that sample? I'll make a thin section and/or polished section, and then return to you the remains of the sample, plus the thin section and anything else I get, for your trouble.
Field relations--well, I'm afraid I can't do that, but someone needs to. I always told my students that the lab samples they had to look at, run tests on, and identify, etc. were just "naked rocks." They were rocks snatched from out of their habitat--out of their natural geological context. And it is true that some of them cannot be identified in hand specimen if that is the only information they get (and I promised not to, and did not, ask them about any of those). We have to determine what the geological context of this material is, and that means field relationships.
Becky Coulson June 07, 2012 06:50PMNorman, I hope Roger and Heath will send you an in-situ sample from the dyke itself; if not, I will visit.
Yes, I hope I have not given the impression that "magnetic anomalies" account for Heath's rocks!! But Heath has referred to periods of "reverse polarization", magnetic studies, etc. in previous notes. Mwandoe's thesis looked like a straight-forward, understandable explanation of magnetic studies and factors that affect magnetism in dyke/sill rocks.
I must add, on Heath's behalf (bless me!) that many authors have indeed classified the Cleveland dyke as an "basaltic andesite", while others say it is a tholeiitic basalt...there does seem to be confusion there. For example, see the photos in thin section at:
Thanks for coming back, Norman. If Heath and Roger have any problems with in-situ samples, let me know exactly how much material and what information you need, and I'll go. I, too, still suspect the ironstone, but some of Heath's photos do not look like ironstone. Anything else we can send as a thank you??
Paul Brandes June 07, 2012 07:06PMI too would be curious as to what a hand sample/thin section of this material looks like. As Norman pointed out, field observations of the material in-situ and its relationship to other rocks in the area must be conducted in order to get to the bottom of this, although thin section analysis will help immensely.....
Anonymous User June 07, 2012 09:51PMIve just read some of the paper and yes its amazingly simmiler to what ive been trying to explain with next to no resources even seems like the paper is edging for the possibillity of what i have stated on my blog that there could be a conection with a period of reversed polorisation or did i read it wrong? Also the deep beck valleys in this area have an amazing ability to preserve rocks and mineralised bones again is it to far fetched for there to be a link?
Becky Coulson June 07, 2012 10:09PMSorry, Heath...it is really is far-fetched. I just wanted you to see what magnetic surveys are about...but it simply does not affect your rocks. The only thing that matters is the mineral content of your rocks, and Norman is willing to make thin sections and check them. For now, let's not slip back into bickering. Perhaps you and Roger can get a fresh hand sample - you need to get a sample from the dyke itself, and not only something you dug up. You also need to pinpoint exactly where it was collected, and ask Roger to help you describe the surrounding rocks. You need to stay on course here - few people pop up and offer to do this! Good luck. Becky
Anonymous User June 07, 2012 10:11PMI would like to add this i was not going to report this on my blog yet but since seeing this paper i think its best, ive found that i can make small pieces of this material spin using a magnet this is what first made me think there could be a connection with reversed polorisation, also some parts of the larger pieces and boulders seem to but ime in no way sure, repel a magnet, now please i would like to say to all with an interest in this subject ime only after answers not a pat on the back, so all differences apart i would aprieciate all the input i can get and please don't be offended if i don't agree with it and ile try to do the same.
Anonymous User June 07, 2012 10:39PMBecky ime not being funny here but have you fully read my posts and viewed the images? the large boulders and stone at the entrance to the quarry covered in magnets are most certainly from the dyke at this location no ifs no buts and as for this thin section stuff a geologist who helps me and one from durham university have been there and got the t shirt so why i need to have the dyke stone at this location re identified ?
Its Basaltic andesite and it atracts fridge magnets, also who exactly is far fetched me or the fella doing the masters he refers to the possible link himself.
All the best Becky Heath
Anonymous User June 07, 2012 11:20PMA total field magnetic survey was conducted in Harwood valley in Northern Teesdale, and the neighbouring area, to investigate the igneous intrusions which could be the cause of a magnetic anomaly and metasomatism in the mineralization of the area. Niccolite and other nickel-bearing minerals had been found in magnetite-rich ore at three localities in Harwood valley by a team of the British Geological Survey. This mineral assemblage has only been sighted in a few other zones and the cause of mineralization was assumed to be metamorphism due to the emplacement of the Whin Sill and associated dykes during the late Carboniferous-early Permian age. Magnetic profiles recently acquired in the area confirm the existence of a dyke intruding the Teesdale fault along the Harwood valley. The average amplitude of the anomaly is 350nT, reversed with respect to the present field. Further investigations to the south-east and north-west of the valley relate the intrusion with the known outcrops of the Cleveland dyke (Tertiary). An outcrop of an igneous intrusion that bears similar properties with samples of the Cleveland dyke rock was recently sighted by the author at lower Langdon Beck near the confluence of the Tees and Harwood rivers. Thin sections of this rock displayed an identical match in grain size and pigment composition with the Cleveland dyke samples from other known outcrops, confirming the dyke's presence along the Teesdale Fault.2.5D modelling of the magnetic profiles was carried out and the results reflect the depth to the top of the dyke at Harwood to be about 30m. Thickness of the body varies from 5 to 25m but is 12m at Harwood and about 14m in Etters Gill. Further south of the valley at Langdon Beck is another geological formation; the Burtreeford Disturbance. This is a series of faulting and folding that was a result of compressional stress (Permian age) from a WSW direction. It also produced the E- facing monoclinal folds of the Dent Fault zone and the easterly directed Pennine thrusts of the Cross Fell Inlier before, during and after the emplacement of the Whin. The study here reflects the Disturbance as a magnetic high and its confluence with the Teesdale fault, the inferred Cleveland dyke and the Whin Sill offers a complex interpretation challenge. A GIS data base for the project area was created using Arc-GIS, GRAVMAG, SURFER,DIDGER and other Microsoft Office applications. General interpretation of the anomalies is conducted but conclusions raise several questions. The cause of the mineralization in Harwood Valley is still uncertain, though it could be due to the cooling Cleveland dyke (58Ma) or the dyke could be forming a passage for the fluids of unknown age from the lower crust or mantle that cool and crystallize at shallower depths.
Item Type: Thesis (Masters)
Award: Master of Science
Thesis Date: 2005
Norman King June 08, 2012 12:20AMRog,
Well, now you see how Heath feels about helping us verify his findings. I remind you about what I am sure you already know, that science works by verification. So I would still like you to collect a sample for me. I need a modest sample, perhaps not quite fist sized, but a couple of smaller samples would also do.
I do not doubt that Heath’s geologist friend received or collected a sample of basaltic andesite, and the rock Heath refers to pictured on his blog page indeed looks like porphyritic basaltic andesite. But there may be some variation in rock collected from the dyke. The texture may be different between the middle and the edges, for example, and there may be some compositional differences as well. It is probably true that all rock bodies vary in one way or another, so there is nothing wrong, and certainly nothing disrespectful, in asking for a second analysis. There has been some discussion in the literature about whether this is basaltic andesite or tholeiitic basalt, and it may be that both rock types are present. That is one reason why nobody ever makes do with a single sample (except if it is a Moon rock!), when many samples could be easily collected. It is also quite possible that the dyke contains xenoliths of foreign material. The dyke follows a fault over much of its path, and repeated displacement along faults may result in the mixing of material from the country rock (surrounding the dyke), and mineral-rich solutions easily flow along fault zones. All of these possibilities should be considered.
Heath’s most recent post is the entire introduction written by Mwandoe to his thesis. Note that my comments and suggestions stem from Mwandoe’s work. In fact, Mwandoe goes on to say that he did not answer the question about mineralization that included formation of magnetite associated with the dyke. Hence our interest.
Rog, If you can collect a sample I will contact you by private message to discuss how to get the sample to me.
Roger Curry June 08, 2012 06:41AMHi Norman et al,
Gonna be very wet today, I'll try to get a sample of the actual dyke, and not hornfels. Will observe geological context as best we can. The magnetic dyke is only part of what Heath has to show me through the driving rain, and of course the boozer will be beckoning, but I'm sure we can provide samples to all who want them.
See you later today Heath mate,
Anonymous User June 08, 2012 09:31PMOh my when i say this stuff is basaltic andesite its becouse thats what it has been studied as being in thin sections !, the city of leeds has tons of it making up its streets Has does the aproach to whitby abbey the very same cobbles i showed my weak magnets attatched to, Norman please check the histort of the rock in any one area before making comment i did inform you of the facts yet you either never read these posts or egnored them, me and Rog visited the sites ive now been studying for the last 5 years and ile now post the images but will let Rog fill in what he viewed on site.
open | download - DSCF1450-001.JPG (116.1 KB)
open | download - DSCF1454-001.JPG (112.4 KB)
open | download - DSCF1462-001.JPG (120.7 KB)
open | download - DSCF1454-001.JPG (112.4 KB)
open | download - DSCF1462-001.JPG (120.7 KB)
Anonymous User June 08, 2012 10:07PMNornan ile put it as simple as i can this cobble was fashioned from the Cleveland dyke at the Stainton village mine it is basaltic andesite and is magnetic as is all the left over basaltic andesite left over from the quarry workings that ended in 1928 please stop this ironstone thing its silly and is not getting us any further forward.
open | download - IMG_0044-001.JPG (147.3 KB)
open | download - IMG_0054-001.JPG (165.9 KB)
open | download - IMG_0056-001.JPG (152.8 KB)
open | download - IMG_0054-001.JPG (165.9 KB)
open | download - IMG_0056-001.JPG (152.8 KB)
Norman King June 08, 2012 11:54PMHeath,
Some of these photos are instructive. BTW, I have looked at all the photos you posted, most of them 2 or 3 times. I have also seen all or most of the photos on your blog page. I did not remember that first view, but it may already be posted somewhere. The first photo today (DCSF1450-001) clearly shows a horizontally-oriented rock body. In other words, this is a sill. Photo IMG_0054-001 and IMG_0056-001 both seem to show a rock that is rich in olivine. That’s why they are green. (Does anyone else out there have an opinion about that?)
Preliminary interpretations: the rocks you showed today are not basaltic andesite of the Cleveland Dyke, rather they are olivine dolerite of the Whin Sill. This is the rock mentioned by Mwandoe as the only rock in the area that is attracted by a magnet. I agree, however, that Mwandoe was not correct about that, and that you are correct about which rocks attract a hand magnet. After all, you have documented it photographically. I think we still need a thin section of what you guys collected to verify all of this, and will await word from Rog about that. It looks to me that this really dark rock you show today is different from the lighter-colored speckled rock in the monument. In fact, I would like to have a piece of the speckled rock, as well as the dark rock from today. I’ll make thin sections of both.
An issue for me is that olivine dolerite has been reported only from the Little Whin Sill, found close to Durham. This is the oldest of the Whin sills, and lies above the younger sills. It is also least evolved, and thus the only one that is olivine-rich (reported at 3-12% olivine). It was emplaced during the Late Carboniferous.
If we can confirm this, it might be the first time an olivine-rich sill has been reported in your study area. This would be a real discovery that can be documented. Hopefully, you will make more such finds with additional work. Certainly with your additional work today, we may indeed be moving forward. Such a discovery can hardly be called “silly.” But you are right--we don't need to argue about this now. Wait until the real data come in (from the thin sections).
However, we indeed still have to look at those samples in thin section, so don’t uncork the champagne bottle yet.
Edited 1 time(s). Last edit at 06/08/2012 11:55PM by Norman King.
Anonymous User June 09, 2012 12:03AMIf ime honest Norman i like you mate but in words us common people use over here your doing my head in ime sick of showing the cobbles for them to be talked around with long words they are from this dyke location please why do you not comment on the magnets stuck to them?
Paul Brandes June 09, 2012 05:25AMBecause Heath, there is nothing more to comment about the magnetism of the rocks!!! You have shown that they attract a magnet; ok that's great, but it's time to move on to more interesting and advanced questions about the rocks in the area. With that said, I only have one last question:
What exactly are you trying to prove with the magnet?
I believe this to be the million dollar question now for everyone....
Edited 1 time(s). Last edit at 06/09/2012 05:39AM by Paul Brandes.
Paul Brandes June 09, 2012 05:43AMNorman,
Two other possibilities for a green-coloured mafic sill (which is what they are) are serpentinisation and epidotisation. After skimming through the available literature, I don't believe either to be the case and that they are indeed olivine-rich mafic rocks, which then is not unusual to have some magnetite in it and therefore, be slightly magnetic. A thin section would really tell the tale here, even if they have been previously done in other studies.
Becky Coulson June 09, 2012 08:40AMPaul, this question is lateral to the discussion at hand, but I noted your recent caveat given to someone about rare earth magnets that "stick to almost anything". Are fridge magnets composites including rare earths? Given that some magnetite may be present in Heath's rocks (whatever they are), would the use of such magnets make them appear to be more magnetic?
I look forward to hearing if Rog and Heath collected samples from the Cleveland Dyke itself. Becky
Edited 1 time(s). Last edit at 06/09/2012 09:18AM by Becky Coulson.
Norman King June 09, 2012 12:29PMHeath,
I noticed in your post at June 06, 2012 10:37 PM you referred to a geologist (I assume) telling you that the basaltic andesite at the quarry (I assume the Stainton Quarry) contains a “certain rare magnetite.” This is reported in the paper by T. P. Young in the Proceedings of the Yorkshire Geological Society, that I already cited for you, to be ferric cronstedtite spinel (see p. 130–the second page of the article). This was actually determined by Dyson and Youell in 1966 (J. E. Dyson and R. F. Youell, 1966, Variations of structure and composition in natural magnetites: Transactions of the Leeds Geological Association, v. 7, p. 223-231). I have already requested the latter article by interlibrary loan–the same way I got the article by T. P. Young.
It turns out that magnetite forms a solid solution series with ulvospinel, which contains titanium in addition to ferrous (reduced, FeO) iron. So this magnetite is leaning toward ulvospinel in titanium content, and it has an unusually large amount of associated ferric iron (Fe2O3). There is nothing remarkable about this kind of “magnetite” mix, although it is probably not in many mineral collections. Cronstedtite is a serpentine mineral (iron silicate), and may indeed be at least part of the reason that the stone is so green (as Paul stated). But, for sure it shows that the rock has been altered. That’s what I have been saying all along based upon the information I have been able to gather about this deposit from you and the literature (and now Ralph Bottrill and Paul Brandes are saying the same sorts of things–how many opinions to the same effect do you want?).
Reading again the passages that Rog sent by George Young published in 1828 (and I hasten to assure everyone that I normally do not use publications of that vintage for anything beyond the kinds of observations reported in this one), he states that “A vein of wacke three or four feet wide occurs in Stainton quarry where the authors also observed some of the most interesting varieties of the basalt.” OK, I will assert that even in 1828, geologists could distinguish a wacke from a basalt. A wacke would most likely be a “clay” rich sandstone, but definitely a sedimentary rock or a weathered rock rich in phyllosilicates (perhaps cronstedtite).
You noted in your posting of June 08, 2012 09:07 PM that the sample you collected are from quarry workings. What was quarried there--Ironstone? Basaltic andesite? Was basaltic andesite refuse from ironstone mining that wasn’t sent to the mill for processing, but used for pavement and rock walls instead?
Finally, I have to agree with Paul that there is nothing to remark upon the magnets sticking to the rock. We have all told you that this is of no note. What else can we say? It's a dead horse, and there is no reason to keep whipping it. But I’ll bite one more time--what do YOU think is so important about that? Becky’s point is important also. I hardly think that cheap refrigerator magnets would contain rare earths, but then maybe they are not just run-of-the-mill refrigerator magnets. We have to consider all possibilities.
And forget the insults and complaints about big words. This has to be an adult discussion. I think we have all taken you seriously from the start. See my comments in the first paragraph. Do you think we haven't gone far enough to help you?
Anonymous User June 09, 2012 01:07PMRoger the origional question i asked was has anyone seen images of a magnet stuck to rocks other than loadstone i produced my many examples of fridge magnets stuck to the basaltic andesite at this location, and an example of a magnet stuck to a sample of rosedale iron stone, as yet ive had no images posted. Just post after post telling me why yourself and others believe the examples i show are other than what ive said they actually are ie Basaltic andesite.
Also please believe me the closest iron stone deposits are in the eston hills about 3 miles north east of here, which helped fuel the industrial reveloution, i repeat if yourself or any other members wish to learn more of the ironstone mining in this area please view A Century in stone, by Craig Hornby www.pancrack.tv.
Ps the colour of the dyke stone here is grey- blue sorry if the pictures seem to show them to look green they look grey blue on my screen.
All the best Heath.
Roger Curry June 09, 2012 01:18PMMy visit yesterday, to see what Heath has discovered, was very interesting. Well worth getting wet and muddy! What an enthusiastic, articulate and friendly man he is. I was made most most welcome in his home, I think his family were glad someone had arrived to "talk rocks" with him. Although he has donated most of his collection to the local school, his back yard is a treasure trove of locally found fossils, rocks and minerals.
His interest began some years ago, when his daughter found an Auroch skull in the banks of the nearby Stainton Beck. He started digging. When I say digging, I mean carefully digging away scores of tons of overlying clays, in several different locations, to expose the Stainton gravel beds. The gravel bed and it's rich collection of diverse fossils is about a 30cm deep, and he has uncovered it at several locations, which can be seen on Heath's map here. The Stainton beck is only a small stream, and has cut down through about 10 meters of soils, clays and down to the gravel beds, then further clays. The beck itself has nothing to do with the deposition. It has, of course, washed away deposits, and so fossils are also found in the stream bed. Heath's blog which describes the finds can be found here, and a discussion in the Geological Deposits thread, here http://www.mindat.org/forum.php?read,11,260543,page=1. His "recent" fossils are crying out for carbon dating. Even just one. Has anyone access to dating equipment?
I have very little knowledge about sedimentology, so I took a video of the "strata" for Norman to look at. As soon as I have time, I'll get it on Youtube and put a link in the Geological Deposts thread. The local geology is described on my maps as Triassic Keuper marl with overlying glacial bed of boulder clay, with some post glacial alluvium beds, and intruded by the Armathwaite-Cleveland dyke of basaltic andesite, with mercia mudstone next to the dyke. To my eye, Heath's diggings, with clearly defined stratified layers, don't look like the sort of boulder clay beneath my feet where I live, a few tens of miles away. Wait for the video Norman, it will show things better, because you're way off interpreting the photo below as "clearly shows a horizontally-oriented rock body. In other words, this is a sill." No it's mud.
Heath then discovered that small magnets stuck to boulders in the nearby Stainton Quarry. Starting in the early eighteen hundreds, basaltic andesite was quarried from the Cleveland dyke to make cobblestones from the tough rock. In Heath's photo below, you see a small boulder embedded in the Stainton gravel bed.
The stream bed is littered with similar black rocks. I smashed off a lump off the one in the photo for Norman. The dyke itself is no longer exposed at the quarry, which is now landscaped, so no chance of any "geological context" work. At the quarry Heath has man-handled some large quarried boulders together next to the path, for visitors to see what was quarried. I clouted a good lump off one of them. The one from the quarry has a much coarser crystalline texture than the one from the gravel beds. Again, I have videos of this which I'll put a link to in this thread. Both attract a magnet. To my mind, the extremely numerous igneous rocks which attract a magnet could not have come very far (from their sheer numbers) and therefore I'd be inclined to think they are from the adjacent Cleveland dyke, and not glacially transported from elsewhere. Wait for the videos.
Anyway, I've got some rock for you to section Norman, just PM me. Neodymium magnets probably will stick to a lot of magnetite bearing rocks as Paul suggested. But Heath noticed this before all of us, I think it is of note, and there remains the question of one particular fragment Heath has. It shows repulsion at one end. In other words it's a magnet. Cleveland loadstone. This specimen needs further investigation.
Thanks for a great day out Heath, and the beers! See you soon mate.
Norman King June 09, 2012 01:30PMHeath,
You asked about other photos of magnets sticking to other rocks besides loadstone. With a lack of positive responses, you have the answer to your question.
Yes, the dyke stone in the wall and the cobbles are indeed gray-blue. The stones you collected and photographed yesterday are dark green. My screen shows colors accurately.
I don't believe that people know all the paces where the ironstone might ocur. They know very well where it was mined, though. But I 'm talking about basaltic andesite vs. altered olivine dolerite.
Norman King June 09, 2012 01:38PMRog,
Now you see why at one time I excused myself from this discussion. I am sorry that I have to do so again. I just cannot continue this foolishness.
But can you arrange to get me the samples I mentioned–one of the dark green rock you found yesterday, and one of the gray-blue basaltic andesite? I will still make the thin sections and report back. In fact, I will post photomicrographs of them here on mindat. Really, I think the possible discovery of olivine dolerite there is significant, and we should verify that.
Roger Curry June 09, 2012 01:52PMHi Norm,
I don't want to get into a "he said that, I said this" discussion. It's all there on these threads for anyone to examine and make their own mind up, should they wish to. I'll certainly send you both types of rock I collected. I would think they are identical in composition, with the coarser grained (quarry) sample being from the slower cooling centre of the dyke, and the finer grained (beck) sample having been knocked off the side by glacial action. I assume you're in the States, so I need to know what minimum size you need, so we can reduce the airmail cost (I'm out of work at the moment).
Norman King June 09, 2012 03:14PMRog,
Now I see that I probably cannot do anything useful from here in Indiana. Apparently, after viewing all of these photos, and reading the descriptions of what you guys have found, I have not been able to conceptualize the geology of the area you are working. And, clearly, there is more than one topic going on here that have gotten mixed up.
I see in the recent photos a resistant bed that appears to have been hammered on the right. It also appears to have broken away along a joint surface. Now I conclude you are saying that the dark green rock has nothing to do with that. Nor does the basaltic andesite. And I conclude from your comments just now that the dark green rock and the basaltic andesite, at that location, are in the form of only stream boulders (that may have gotten to the area by glacial transport?–as you state, the stream is a small one).
I think, however, that olivine dolerite in place has not been reported in that area. But if it was ice-rafted in, all bets are off on its significance.
I cannot work that out without spending time there in the field. That leaves little room for anything else to be ascertained. Nothing that Heath has described previously is anything beyond what is already known in the area. I would not have expected magnets to stick to the basaltic andesite, but I guess they do. It's curious, but otherwise it doesn’t concern me. I hope my comments on the sedimentology of the bone beds will be useful.
I will certainly look at the videos. If I still think it will serve any purpose to make thin sections, I will let you know, and will pay the postage to get samples here. Otherwise, I really am getting behind on other topics, and need to get back to them because the clock is ticking.
Paul Brandes June 09, 2012 03:51PMOk Heath, this is good; now we're getting somewhere... ;-)
Great job describing the area, Roger!! I will very much look forward to the videos to see what you found. I hope to get over to England next spring and would love to explore that area further. Although I'll be in the Oxford area, I always have a few days after to roam.
Roger Curry June 09, 2012 03:59PMOK.... Norm has bailed.
Anyone else want these rock samples to do a section or, if was it a fruitless exercise, I'll just bin' em.
Neither Heath nor myself asked you to to to any practical work - you asked for them because you didn't believe it was basaltic andesite. We don't care, as Becky had already found photomicrographs of the rock here and Heath knew what the rock was right from the start. Review the threads.
In essence Norm, you've learned something (however trivial you now think it is), i.e. your statement "His reports of the rock being highly magnetic also did not seem to me to represent any plausible igneous rock of which I am aware." from thread "highly magnetic dykes--NOT!"
Blunting my geology hammer for you will not happen again,
Thanks for nowt "mate"
Nathalie Brandes June 09, 2012 04:27PMRog,
I'd be more than willing to take a look at the samples and have a thin section made of them. All I ask is that a good description of where the rocks were sampled is included. Let me know which one was sampled from the streambed cobble and which one came from bedrock. I don't think time is an important factor, so send them as cheap as possible. (I'm a college professor, we don't get paid much in the States). I will reimburse you for your trouble. PM Paul for more information.
As Paul said, we will probably be in England next year. After my work is done, I would very much like to meet you and see this area in person. I am more familiar with the geology of Scotland and Wales, but always look forward to seeing new area. I'm sure you could show me some interesting things and we could have some interesting discussions over a few beers.
Professor of Geoscience
Anonymous User June 09, 2012 06:37PMThanks for the posts Rog and don't forget ya told the kids you would take em down them mines! ;-) as for what Norman had to say well first i still don't know were this green rock is? secondly i think it is quite important to understand the reasons that this section of dyke easily attracts magnets for the simple reason that we don't yet know why.
Nathalie i take it you don't whant to meet me on your trip? this would be a pitty as i would like to show you and paul around, please believe Rog when he says ime a good guy.
But anyway as i say i would warmly welcome any member or anybody else for that matter and show them what ive found, and listen and learn from them, The mannor of my posts may well not help but ive been at this for 5 years now with very little help, and maybe that's making me a bit grumpy as my kids and grandkids call me.
Becky Coulson June 09, 2012 06:42PMRog, Norman was the first, and has been the most consistent, in taking interest in Heath's finds and encouraging him - see the thread on geological deposits. No one doubts that Heath has found rocks that will hold magnets. The question is, what are the rocks composed of, and (perhaps more importantly) what is the exact source of these rocks? Two big, confounding factors in Heath's area are the glacial deposits and the presence of ironstone - most of the dyke rock quarried is either in direct contact with ironstone, or has intruded through it.
Nathalie is willing to do thin sections of your rock samples, and that's great. The problem is, she may be able to identify the rock, which will be fascinating, but you simply cannot state that the rock came from the Cleveland Dyke. Heath's excavations are full of glacial debris...including similar whin sill cobbles and other debris from across the north and west UK. (In nearby Hartlepool, glacial debris and fossils have been shown to have been transported from Scandinavia!)
Please bear with me, and consider this: boulders of Shap granite (glacial erratics from Cumbria) are found in N. Yorkshire. Surely, you could send a sample for analysis, but would you then claim that Shap granite outcrops somewhere in Yorkshire??
This is why, if you want to nail down the Cleveland Dyke rock, the samples must come from the dyke. Just 4 miles southeast of Heath, there are good exposures of the dyke. To make your effort "verifiable" has nothing to do with Heath's credibility or honesty. If we take a sample from the dyke wall, and label it in detail, then anyone can REPEAT and verify the information - they'll be able to return to the same place, take a sample, and get the same results. That is what science demands, and that is what Norm has been trying to say.
One more thing. The thin sections I referred to were offered to help everyone understand why Heath refers to Basaltic Andesite. I don't think that there is anything in those sections that explains the magnetism. Best wishes, Becky
Becky Coulson June 09, 2012 06:48PMNathalie and Paul, If you do want a few days in the north of England, you would be most welcome to stay with us - send us a PM anytime, and I'll give you our email address, location, and give a bit of introduction. One thing though - you must go meet Heath!
Best wishes, Becky
Anonymous User June 09, 2012 07:46PMNorman i can assure you that we do indeed know were the iron stone deposits occure in this area, Teeside was built becouse of these deposits, it was a bit like the gold rush round here people came from all over britain and europe to dig it out of the Cleveland hills and North york moors. its descovery actually contributed greatly to the industrial revalution.
Edited 1 time(s). Last edit at 06/09/2012 07:59PM by Heath Barnes.
Nathalie Brandes June 09, 2012 07:59PMHeath,
Several posts ago (although it might have been in a different thread) I mentioned that I would love to see what you are working on. I guess I just didn't think to re-state that. As I said before, I think seeing things in the field would solve many of the questions posed here.
And Heath, I'll buy you a pint as well. Some of my best work has been accomplished discussing things with colleagues over a pint.:)-D
Thank you very much for the offer. It is most generous. Nothing is certain yet, but it looks favourable that I'll be back in England for at least a little while next year. If I'm there, Paul and I look forward to meeting everyone and seeing some neat geology.
Professor of Geoscience
Anonymous User June 09, 2012 08:04PMBecky your right most of the dyke in thisarea has intruded through ironstone, to the south east of here, but not here it was triassic mudstone then sandstone it intruded here, yet this section is the most magnetic? i was asked to examin the dyke by a geologist from the riggs group and walked the full lenght from stainton to cliff rigg and my findings were that the stainton dyke stone was by far the more magnetic.
Norman King June 09, 2012 10:15PMFolks,
I’m probably the last person you wanted to hear from at this time. But let me say that I am utterly baffled by the continuing conversation. Thus, what more could I do?
Also, Rog, my comment about “no such igneous rock” referred to actually turning it around because of its magnetization. I stand behind my opinion that there is no such igneous rock that will do so without something having been added to it along the way.
Nevertheless, there simply isn’t anything more I can do with the information I have now or will be able to get. I fear I cannot answer any of the questions without being there in the field. But I am going to “stay on the frequency” and monitor progress.
Jolyon & Katya Ralph June 09, 2012 10:53PMHeath.
Can you answer this one simple question before continuing.
How do you know 100% that the rock you claim is basalt or andesite is indeed volcanic and part of the sill, and not some iron-rich hard sedimentary rock that you are mistaking for volcanic rock?
Anonymous User June 09, 2012 11:27PMJolyon the report from Rog should be enough in my mind, but also the cobble is from the basaltic andesite dyke as are the pics of kids magnets stuck all over the rock at the entrance to quary a quarry were basaltic andesite was mined for road stone! as ive stated many times! also ive worked along side geologists at this site at Stainton who have spent there life studying the dyke in this area who's job it is to know all about the geology of this area, yet the magnetic attraction is news to them ie the riggs group.
Jolyon please may i ask have you viewed the links i have shown on the iron stone depositsof this area before asking me this question after all why should i answer this question time and time again ? Here we go again !
Roger Curry June 10, 2012 12:12AMHi Jolyon et al,
I've been somewhat perplexed by your replies to Heath. Please PM me and I will send you the rocks. Field geology rules! It seems simple to me. I'm just someone who is into unusual fluorite from the dales, I'm not a rock man.
Dennis Tryon June 10, 2012 01:33AMI intend to check all further posts, and will have nothing to do with any that contain more than 2 comments from Heath Barnes.
I have read this one completely and am left in total confusion. I can't even tell if he is asking a question or making a statement.
Maybe a spell checker would help a little.
Edited 1 time(s). Last edit at 06/10/2012 01:38AM by Dennis Tryon.
Anonymous User June 10, 2012 02:38AMI see i have to entice certain members to do as i said if they require info on the iron deposits here ! instead of just viewing this!!!
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Anonymous User June 10, 2012 02:56AMDennis Tryon Wrote:
> I intend to check all further posts, and will have
> nothing to do with any that contain more than 2
> comments from Heath Barnes.
> I have read this one completely and am left in
> total confusion. I can't even tell if he is asking
> a question or making a statement.
> Maybe a spell checker would help a little.
Edited 1 time(s). Last edit at 06/10/2012 02:57AM by Heath Barnes.
Anonymous User June 10, 2012 03:08AMIf i was good at spelling mate i might not of found this lot! ps i don't use a spell check on forums for one reason only that is it puts my comments and Wiki proffesors like you in different sides ie i can not spell so what i right can be trusted but good spelling can be pasted from anywhere call it my signiture but boy it works wiki fella !
Becky Coulson June 10, 2012 07:08AMNorm,
I also will back away for the moment, unless I can provide relevant and helpful information. It will be interesting to see if we get thin sections of the rocks that Heath and Rog have collected, as there isn't much more to discuss until those are supplied. When our own field work ends in late July, I will go to the dyke exposures and collect samples; I'll send you a PM at that time to ask if you are still interested.
Heath, the Redcar mudstones consist of four layers, including pyritous shale and ironstone shale.
Best wishes, Becky
Edited 1 time(s). Last edit at 06/10/2012 07:49AM by Becky Coulson.
Ralph Bottrill June 10, 2012 05:01PMI must concur with Norm and others in being totally confused. This thread is a train wreck! There is a lot of fuss about some magnetic cobbles that may or may not derive from some local dykes or sills or maybe ironstones or other rocks, or maybe they are glacial and from over the hills and far away? Are any of the dykes or sills magnetic? If not how do you know they are related to the cobbles? Thin sections of all these rocks and cobbles may be required to se if they are related, but maybe just one of the cobble to see what that is would be a good start.
Anonymous User June 10, 2012 07:53PMRalph is this simple enough the cobble was crafted as were thousands more from the Cleveland dyke here at Stainton quary, a quarry like many others along the line of the Cleveland dyke, a dyke made up of basaltic andesite!, the cobble like many others here easily atracts kids magnets and weak fridge magnets.
There are no ironstone deposits in this part of south west Cleveland!
The bed rock here is mercia mudstone ( Triassic) and the basaltic andesite that is now the cobble and boulders in the quarry that have my and Rogers magnets stuck to them, intruded through the mercia mudstone and a sandstone at this location (( Stainton Quarry ) about 59 mya.
There are no reports that i am aware of nore the geologists helping me that state nor show magnets of any strength being attracted to the basaltic andesite at this nore any other location along the full extent of the Cleveland dyke.
If you would like anything else explaining i am more than happy to do so. All the best Heath.
ps one of the comments i personnaly found the most confusing was when Norman insisted that the red plastic lower clay deposit Roger was pictured kneeling on while pointing the gravel bed at my main excavation was in fact a sollid rock sill !
Anonymous User June 10, 2012 09:25PMEmplacement of the Cleveland Dyke: Evidence from Geochemistry, Mineralogy, and Physical Modelling
R. MACDONALD1, L. WILSON1, R. S. THORPE2 and A. MARTIN1
The igneous rocks of the British Tertiary Volcanic Province (BTVP) comprise intrusive central complexes and associated lava fields in northwest Scotland and northern Ireland. These centres are associated with linear dyke swarms which are radial around the major central complexes. The most extensive dyke swarm is related to the Mull intrusive complex and includes the Cleveland dyke, which appears to extend some 430 km from Mull through the Scottish Midland Valley (SMV) to the coast of northeast England. The dyke may have been emplaced by lateral magma migration from Mull, by vertical magma migration, or by a combination of these processes associated with the emplacement of the Mull centre and the presence of a regional stress field in northern Britain.
Petrographic, mineralogical, and geochemical data for samples collected across and along the Cleveland dyke have been used to evaluate its petrogenesis and emplacement mechanism. The segment of the dyke north of, and along, the Southern Uplands Fault, the southern boundary of the SMV, is not comagmatic with that to the south, which is now defined as the Cleveland dyke sensu stricto. The Cleveland dyke is an olivine-free, plagioclase- and pyroxene-phyric basaltic andesite. Plagioclase mineralogy and bulk composition indicate that it experienced a complex magmatic history involving polybaric fractional crystallization and minor crustal contamination. Despite this complex evolution, the dyke magma is relatively homogeneous and shows chemical characteristics closely similar to tholeiitic rocks from Mull. The data substantiate lateral emplacement from this BVTP centre, rather than by vertical emplacement through heterogeneous lithosphere.
Numerical modelling of dyke dynamics is consistent with emplacement of the Cleveland dyke as a single pulse of magma from the Mull centre, flowing in a manner transitional between laminar and turbulent conditions. According to this model, the dyke (volume c. 85 km3 was initiated in a large magma chamber below Mull subject to a small excess magmatic pressure. Lateral migration at relatively high velocity (1–5 ms−1) caused emplacement of the dyke in 1–5 days. Following emplacement, minor vertical ascent of magma may have contributed to the local en echelon distribution of dyke segments.
© Oxford University Press
Hope this helps solve the confusion this paper is describing the stone both cobble and boulder that the magnets are attatched, also please note Norman its reported as being olivine free !
Anonymous User June 10, 2012 10:01PMCleveland Dyke from Wind Hill quarry (NZ 7597 0643), near Wind Hill Farm, North Yorkshire. The dyke is one of the Tertiary swarm emanating from the isle of Mull, Scotland, no doubt caused by crustal tension during the opening of the Atlantic which eventually separated North America from North Western Europe. A is a photograph of a thin section in plane polarised light. Opaque minerals of iron oxides and a cloudy cryptocrystalline mesostasis (e.g. bottom near centre) are apparent as well as a high relief mineral at the near centre.
B is the same thin section under cross polarised light. The Cleveland Dyke is classed as a basaltic andesite. It is a porphyritic rock with small (1-2mm) phenocrysts of plagioclase feldspar. The groundmass is seen to consist of laths of plagioclase (grey-black interference colours and the pyroxene, augite (blue, purple & yellow interference colours). The near centre shows what appears to be an olivine. It measures 1mm in length NW-SE. Further analysis, however, e.g. its almost uniaxial interference figure, indicates that it is a type of augite known as pigeonite. The literature states that this dyke is olivine free.
Sorry the image below would not paste.
The photo on the right shows part of the dyke wall, on the right, in contact with Lower Jurassic sediments (Cleveland Ironstone Formation), on the left. Presumably part of the dyke was left there to act as a retaining wall.
The photo on the left is a polished section of Redcar Mudstone Formation taken from within a few feet of the dyke contact. Normally it would be a dark gray shale or mudstone. However it has been thermally altered resulting in the "spotting" as well as induration. There does not appear to have been any detailed published analysis of the spots, but it is thought that they could be the result of coagulation of the hydrocarbon content within the mudstone.
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Back to thin section thumbnails
I also hope this helps but please note that these thin sections are from a part of the dyke that intruded ironstone deposits, unlike the stainton section i have the magnets attatched, Although i can say ive visited cliff rig that also intruded through iron ston deposits and did find some basaltic andesite left over from the mining that did atract the magnets, but in no way as potant as the atraction at Stainton quarry.
And yet again Norman its reported as olivine free !
Edited 2 time(s). Last edit at 06/10/2012 10:12PM by Heath Barnes.
Anonymous User June 10, 2012 10:22PMRalph Bottrill Wrote:
> I must concur with Norm and others in being
> totally confused. This thread is a train wreck!
> There is a lot of fuss about some magnetic cobbles
> that may or may not derive from some local dykes
> or sills or maybe ironstones or other rocks, or
> maybe they are glacial and from over the hills and
> far away? Are any of the dykes or sills magnetic?
> If not how do you know they are related to the
> cobbles? Thin sections of all these rocks and
> cobbles may be required to se if they are related,
> but maybe just one of the cobble to see what that
> is would be a good start.
Sorry Ralph missed your question there ie i know the cobble is related to the dyke becouse hard working men mined then fashiond it from the basaltic andesite dyke that is the Cleveland dyke Stainton. Then i descovered i could attatch a kids magnet to it.
Ralph Bottrill June 11, 2012 12:20AMHeath, that makes more sense now, I thought you had a stream cobble. If you are working in a quarry you need to run over the working face with a magnet and see where it's magnetic - in contact zones, xenoliths etc.? A cobble in a quarry can sometimes be dumped from another source too. As Norman said, the site description and in situ relations are critical, loose cobbles are a last resort.
Edited 1 time(s). Last edit at 06/11/2012 12:23AM by Ralph Bottrill.
Norman King June 11, 2012 01:40AMMagnetite and ilmenite are opaque (black) in polarized light, so there appears to be about 5% magnetite or ilmenite showing in the thin section. That isn't enough to explain the more extreme magnetic properties you mentioned, but it may be enough to cause a strong magnet to stick to it. (Does anyone have a feel for that–whether 5% is enough?). In all the reports I have seen, the Cleveland dyke is reported to contain magnetite.
This has nothing to do with the dark green rock you pictured earlier, however–the one I said looks like it has olivine in it (but may also contain epidote and/or serpentine--thin sections would tell us). But we still don’t have any information on where that rock ultimately came from.
Roger Curry June 11, 2012 01:51PMHi All,
I've uploaded the video from last fridays visit to Stainton. You can see it here. I removed the sound, as Heath and I were talking on unrelated topics. It's 2mins 42 sec. Sorry I didn't have time to do any editing, so the magnet bits go on.. and on..
Sorry also for the appalling camera-work!
Stainton Quarry & Beck, Cleveland. Friday 8th june 2012.
(1) Heath Barnes shows neodymium magnets sticking to a basaltic andesite sign at the quarry entrance.
(2) His diggings showing the sediments above and below the fossil-bearing Stainton gravel beds.
(3) A boulder of suspected basaltic andesite in the Stainton gravel beds.
(4) Quarried boulders of basaltic andesite from the Cleveland dyke.
(5) Two rock samples. The coarse grained rock is from the boulder which Heath throws the magnet on. The finer grained rock is from the boulder shown in the gravel beds.
On my monitor the rocks appear to be more green than they are visually. I have very little knowledge of petrology or sedimentology, so it's up to you guys to interpret what you see. I still have the samples if anyone is still interested in doing thin sections.
Ralph - "This thread is a train wreck!" I totally agree mate!
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