Learning Center What is a mineral?The most common minerals on earth Information for Educators Mindat Articles The Elements The Rock H. Currier Digital Library Geologic Time

Minerals by Properties Minerals by Chemistry Advanced Locality Search Random Mineral Random Locality Search by minID Localities Near Me Search Articles Search Glossary More Search Options

The Mindat Manual Add a New Photo Rate Photos Locality Edit Report Coordinate Completion Report Add Glossary Item

Mining Companies Statistics Users Mineral Museums Clubs & Organizations Mineral Shows & Events The Mindat Directory Device Settings The Mineral Quiz

Photo Search Photo Galleries Search by Color New Photos Today New Photos Yesterday Members' Photo Galleries Past Photo of the Day Gallery Photography

Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

LocalitiesDiamond Lake, Herschel Township, Hastings Highlands Municipality, Hastings County, Ontario, Canada

27th Nov 2016 00:59 UTCReiner Mielke Expert

What proof is there that this is augite? It all looks like diopside to me. I know of no verified augite from any calcite vein/dyke in Ontario or Quebec.

27th Nov 2016 01:23 UTCAlfredo Petrov Manager

As augite is really just "dirty diopside", with lots of substitutions and disorder, does it really matter? If it's light-coloured and translucent, I'd call it diopside; if dark and opaque, then it's probably "augite". The definition of "augite" is a mess, and includes both Mg- and Fe- dominant members, in violation of normal species naming conventions.

Normally I'm a stickler for correct naming of species, after analysis, but in the case of something as illogically defined as augite, I'm tempted to say "Who cares?"

27th Nov 2016 12:49 UTCReiner Mielke Expert

Exactly so it should all be called diopside. However if one is going to call something augite then one had better prove it is "dirty" with analysis. Color is not reliable. For years people had been calling the diopside from Otter Lake http://www.mindat.org/photo-505755.html augite because it was black but analysis showed it was diopside. There are still samples out there with the augite label. Once someone calls it something it takes on a life of it's own and is diffficult to kill even if the reason for calling it that in the first place is dubious.

Here is another good example http://www.mindat.org/forum.php?read,105,398393,398394#msg-398394 so difficult to kill that not even Mindat wants to do it.

27th Nov 2016 13:31 UTCAlfredo Petrov Manager

I agree, Reiner. The problem is the cost of analyses. With the current state of the technology we can assume that only a tiny fraction of mineral specimens in collections will get analyzed. With some large classes of minerals (tourmalines, amphiboles, sulphosalts...) many analyses will be close to useless even if carried out. What to do with the majority of specimens that remain unanalyzed? ...or inadequately analyzed?

Basically we tend to stick to field terms to label these, and I don't think that's necessarily such a bad thing, as long as we keep in mind that that is what's being done. How many purpurites are really heterosites? How many actinolites are really tremolites? How many "piemontites" are really just red epidotes or clinozoisites? How many epidotes are really clinozoisites? How many schorls and uvites are really dravites? How many "ankerites" are really Fe-rich dolomites? What percentage of grey needles are a different sulphosalt than what is written on the label? How many of the "native platinum" photos on Mindat are really mixtures of Pt-Fe alloys? ...and so on and so on. The list of prone-to-misidentification minerals is endless. When a locality has been studied in detail by a mineralogist, we can then probably specify which identifications are wrong. But for unstudied localities (the majority of localities) we can't do that. Then do we demand that photographers pay for an analysis of every amphibole, tourmaline, sulphosalt, garnet, etc etc that they upload or we'll question the photo? I don't know; perhaps we should. But I suppose an extreme step like that would just discourage people from collecting, or uploading photos, and all we'll get from then on will be photos of quartz and pyrite.

I just keep a skeptical "?" in mind when reading any species label, but I can't demand analytical proof from every photographer on Mindat. And what would an adequate level of proof be anyway? Many photographs on Mindat just say "analyzed" on the caption, and I suspect you, Reiner, would be the first to agree that that is a useless statement. We really need to know who analyzed it, by what methods, and what were the actual numerical data, in order to adequately assess the likelihood that the ID is correct. We might have that level of evidence for a few tens of photos, out of the more than three quarters of a million already uploaded to Mindat.

27th Nov 2016 22:48 UTCDoug Daniels

Well that does it. As soon as I win the lottery, I'm having every one of my specimens analyzed in detail. May not have any specimens left, but at least I'll know what they were.

27th Nov 2016 22:55 UTCReiner Mielke Expert

You don't need to analyze in detail, simple semi-quantitative EDS for 10-20$ will do. It is easy to differentiate a "dirty" diopside from a "clean" one with this.

28th Nov 2016 02:08 UTCDoug Daniels

I was being a facetious jack-o-lantern - would analyze EVERY specimen, no matter what, just to have the paper trail. Again, there likely wouldn't be any physical specimen left, but by golly we'd know what it WAS.

28th Nov 2016 05:54 UTCVachik Hairapetian Expert

I just received a XRF analysis on nice "augite" crystals from Hormoz Island, S Iran. It was known to be augite for several decades but I will do an EDS to see if these are diopside too. However, weight percentages from XRF revealed SiO2 (53.76%), MgO (13.37%), Fe203 (13.3%), CaO (16.5%), Na2O (0.55%), Al2O3 (13.37%), TiO2 (0.17%). It is interesting that XRD revealed diopside!

28th Nov 2016 11:23 UTCReiner Mielke Expert

According to Mindat :"The modern definition of augite is that it is relatively low in calcium with some disorder of occupancies of Fe2+ and Mg in both octahedral sites. Fe:Mg may vary from 0 to 1 by definition." Trouble is this is rather vague. Exactly how low does the Ca have to be to be augite?

28th Nov 2016 11:53 UTCReiner Mielke Expert

"It is interesting that XRD revealed diopside!" That is because it is diopside, just a "dirty" one which some people like to call augite. But how "dirty" does it need to be to be augite? That is the problem.

29th Nov 2016 15:02 UTCAndrew Debnam 🌟

Hi Reiner, I was not aware of the info below. As I am sure you aware a fair amount of material from the Bancroft area comes with an Augite attribution. Diamond Lake comes to mind. Is it fair to say this maybe or is erroneous?

Andrew

http://www.mindat.org/gallery.php?frm_id=pager&cform_is_valid=1&min=419&loc=&u=&potd=&pco=&d=&showtype=1&phototype=0&checkall=1&loctxt=ontario&keywords=&orderxby=&submit_pager=Filter+Search

Reiner Mielke Wrote:

-------------------------------------------------------

> What proof is there that this is augite? It all

> looks like diopside to me. I know of no verified

> augite from any calcite vein/dyke in Ontario or

> Quebec.

29th Nov 2016 17:22 UTCReiner Mielke Expert

The default designation should always be diopside. Unless you have some proof it is augite that term should not be used, case in point is the Diamond Lake occurrence. Someone took it upon themselves to call it augite and everyone followed the leader. I sure would like to know who the leader was and why he called it augite.

If I can get a hold of a small piece I intend to get it analyzed.

29th Nov 2016 18:00 UTCAndrew Debnam 🌟

The Bancroft chamber of commerce mineral collecting guide book may have played a role in this notion. It states Augite is a common mineral in the Bancroft area and lists it being present at the Musclow Greenview road cuts , Schickler Fluorite location and the North Baptise Lake occurrences. I am not sure if people have looked at streak-Augite-Greenish gray, light to dark brown, Disopside-white to jump to a conclusion. I have some material from Diamond Lake if you would like a piece.

29th Nov 2016 18:29 UTCReiner Mielke Expert

Hello Andrew,

This is the same book that attributed green fluorscence to autunite of which there is none, so you have to be wary of that book. If you can send me a tiny clean and fresh piece around 1mm in size that would be great. You can just tape it to the inside of a Christmas card. Maybe best to send me several that size so I can select the best piece for EDS. If you have any other "augites you would like analyzed from Ontario feel free to include them. I will PM you my address. Thanks

29th Nov 2016 19:52 UTCAndrew Debnam 🌟

Thanks Reiner, will do.

2nd Dec 2016 21:24 UTCRalph S Bottrill 🌟 Manager

Augite is not really dirty diopside, you can have very impure diopside thats not augite, or an almost Fe-free augite. Augite is a clinpyroxene with between 20-45mol.% Ca in the A site, Mg/Fe ratio irrelevant. You can see the compositional field on the augite page. Surprisingly the IMA dont seem to want to fight the petrologists on this one, but its hard to defend a species designation like this.

3rd Dec 2016 00:45 UTCReiner Mielke Expert

Well both are clinopyroxenes and the diagram gives the Diopside-Augite boundary at a Ca:Mg ratio of 45:55 or 0.82. According to that diagram diopside cannot have a Ca:Mg ratio of greater than 1 and augite is between 0.25 and 0.82 However if you calculate the Ca:Mg ratios for the examples of Augite that the Handbook gives http://www.handbookofmineralogy.com/pdfs/augite.pdf , according to that diagram they are diopside? How do you explain that? In fact one has a ratio of 1.38 so it isn't diopside or augite?

3rd Dec 2016 01:00 UTCReiner Mielke Expert

Hello Ralph,

Do you have an example of very impure diopside that is not augite? I can't find one, or maybe I should say define very impure.

3rd Dec 2016 03:49 UTCRalph S Bottrill 🌟 Manager

Exactly Reiner, but you can have a diopside with 49.9mol.% hedembergite, plus substantial Mn, which i would class as impure and itis still diopside as long as Ca is >45 mol% of the A site. I dont have any texts to hand but am sure Deer, Howie and Zussman would list quite a few.

3rd Dec 2016 04:02 UTCRalph S Bottrill 🌟 Manager

Sorry, nearly missed the previous post. The first analysis has 38 mol% Ca from the formula, the second 45. So the first can be definitely classed as augite, but the second looks borderline, and can be equally categorised as diopside or augite, based on its formula, even though the high Ti content is typical of "titanaugite". But with the latter, if you recalculate the Ca, Fe and Mg, ignoring other components, you get Ca ~0.5, So yes its misclassified and is a titaniferous diopside.

3rd Dec 2016 12:22 UTCReiner Mielke Expert

The only consistent difference between the two is that Augite is Mg deficient relative to Diopside. In other words more substitution for Mg in Augite aka "dirtier".

3rd Dec 2016 12:40 UTCPeter Nancarrow 🌟 Expert

It's really a matter of whether you are coming at it from the pure mineralogist's or the petrologist's point of view, which criteria you use for a pyroxene classification, and I have sat in both seats at different stages of my career.

As I recall from my dim & distant days in petrology, when the purpose of the a large number of microprobe analyses was to charaterise different members of an intrusive igneous complex for example, assuming no other information regarding actual site occupancy is available, when allocating a pyroxene analysis to its pigeonhole in the Ca/Mg/Fe triangle, the simplistic convention is (was?) that any significant quantities of transition metal cations found were summed with the Fe.

Therefore, although considering Ca/Fe/Mg ratios alone may have placed a pyroxene analysis in the diopside field, adding the total of Ti, Cr, Mn etc ions present to the Fe could shift it into the "augite" field. Of course the charge balance juggling required when significant quantities of Na, Al, Ti, Cr, Mn etc were present added another level of complexity!

So yes, the nomenclature is rather vague, and it's not a definitve answer to the OP from me I'm afraid! Simply all part of the fun of dealing with what I call the "dustbin" mineral groups such as the pyroxenes, tourmalines, feldspars, which can mop up such an enormous variety of elements into their structures.

Pete N.

3rd Dec 2016 12:51 UTCReiner Mielke Expert

Of course there are exceptions http://rruff.info/augite/names/asc/R070231 and why is this augite? http://rruff.info/augite/names/asc/R061086

3rd Dec 2016 21:21 UTCRalph S Bottrill 🌟 Manager

Thats true Peter, plus petrologists will tend to lump all dark green-brown black clinopyroxenes in igneous rocks as augite unless analysed. Or if its pink in thin section its titanaugite.

Reiner, the first RUFF analysis is clearly augite, the second is again borderline between augite and diopside; diopside should have Ca>0.9 for 6 O.

Augites are usually more Fe rich than most diopsides but that doesnt make them dirty and doesnt discriminate the two, its all about Ca.

4th Dec 2016 00:58 UTCReiner Mielke Expert

Hello Ralph,

Is that what they call the 10% rule? Must have been what they were using for this diagram LOL.

4th Dec 2016 12:42 UTCRalph S Bottrill 🌟 Manager

Reiner, the (Fe, Ni, Co)As2 ternary diagram is subdivided mostly by structural variations not random numbers like the Ca-Mg-Fe pyroxenes, so its quite different. You could show something similar with pyroxenes, where this is a structural change between augite and pigeonite, and enstatite-ferrosilite, but it doesnt quite match the mineral fields shown, so its a total shambles really!

4th Dec 2016 13:13 UTCReiner Mielke Expert

Hello Ralph,

Actually the diagram is based on chemistry and has no validity in terms of the usual accepted IMA definitions, much like the augite-diopside diagram. Either way neither of them make much sense. I find it strange that the IMA is such a stickler for other minerals such as the amphiboles and pyrochlores but so lax in this case.

4th Dec 2016 14:00 UTCAlfredo Petrov Manager

"The IMA" in these cases is a rather imaginary concept. Such decisions are made by subcommittees of people working on whatever group they happen to specialize in, not by "the IMA" as a whole, so there won't be much (if any) overlap between members of different groups. Hence the lack of consistency. Some groups follow IMA species rules and split species strictly according to site dominance (hence the demotion of intermediate plagioclases from species to mere varietal status), other committees find reasons to be more favorable to the concerns of petrologists or clay mineralogists, etc. Not necessarily a bad thing, although my personal preference would be for consistent application of the site dominance rule.

4th Dec 2016 20:37 UTCRalph S Bottrill 🌟 Manager

Reiner, what your diagram shows is a ternary phase diagram that is used to show how chemical variations in that system control the fundamental crystal structures. Most of the field is blank indicating that if you tried to crystallise a composition from a melt in that area, you would get a mixture, so just subdividing the diagram using the 50% rule gives you an unrealistic picture of mineral compositional fields. They always depend on temperature and pressure though, and other components, so its very complex. Look up phase diagrams for simple series like Cu-Zn and Fe-Ni, they are more complex than we usually consider, site dominance does not work and we just dont always describe the actual phases precisely. We need structural as well as chemical analyses as some of these structures are metastable at room T and P.

4th Dec 2016 21:47 UTCReiner Mielke Expert

Hello Ralph,

The diagram is based on phases that exist at room temperature. See diagram below. They are not metastable phases. I have discussed this over the past 7 years on Mindat and find myself coming back to it from time to time. The last discussion led me to conclude that the 50:50 rule applies and not the 10% rule that allowed a mineral called safflorite I. So are you suggesting that in this case the 10% rule applies and that I need to relabel my lollingite samples with more than 10% cobalt, safflorite? Do I call my rammelsbergite samples with 40% cobalt and 60% nickel? safflorite?

5th Dec 2016 04:21 UTCJeff Weissman Expert

Reiner - others may have better explanation. Your first ternary diagram was most likely made using mixtures prepared from pure end-member components and in a highly controlled lab setting, resulting in an ideal phase diagram with cleanly separated compositional domains. The second is from analysis of natural material which is impure, probably non-stoichiometric (think smaltite or chloanthite) and either meta-stable at compositions outside of the stability ranges given in the first diagram, or likely mixtures of all three, even if the outward appearance is a single crystal or uniform appearing. You would need to make polished sections and do elemental mapping with SEM to determine which of loellingite, rammelsbergite or safflorite are present and how pure or impure they are. Likely other minerals are present as well, so simple EDS analysis of what is essentially bulk samples are not sufficient, you need to analysis individual micron-sized or smaller grains to get a better picture of what may be in a given sample.

With regards to augite - without detailed characterization, diopside is just as good a name as augite. But don't get me started on aegirine-augite or even ferroactinolite/actinolite :-S

5th Dec 2016 12:41 UTCReiner Mielke Expert

Hello Jeff,

The first diagram was not prepared using only synthetic phases but mainly natural ones supplemented by synthetic ones. Also the first one does not represent stability ranges but simply known compositions at room temperature and is by no means comprehensive. The second was creating using a microprobe and polished sections as you suggested and the analyses do not represent mixtures. Although in many cases these compositions occur in zones within a single crystal.

If you want to know the details of these diagrams I suggest reading the paper these came from http://rruff.info/doclib/cm/vol11/CM11_150.pdf

or you can just take my word for it.

5th Dec 2016 14:48 UTCJeff Weissman Expert

Hi Reiner, I took a quick look at the reference given in the caption for your Figure 100 (Radcliffe and Berry, 1968) - see http://rruff.info/rruff_1.0/uploads/AM53_1856.pdf In this case the phase behavior of lollingite, safflorite and rammelsbergite were based initially on natural specimens, and then confirmed with synthetic specimens, especially for determining the limits of solid solution between the three - clearly natural Co-Ni-Fe-As minerals are rarely single phases, mostly mixtures. However, we really should continue this discussion on a different thread, and get back to the augite issue in this thread.

5th Dec 2016 16:09 UTCReiner Mielke Expert

Hello Jeff,

The reason I brought it up was the "10% rule". I have no interest in discussing safflorite further as it is a dead horse as far as I am concerned. I will stick to the IMA 50:50 standard for the diarsenides. As for augite, it is not up to us to change things, we will just have to live with the craziness.

6th Dec 2016 11:14 UTCRalph S Bottrill 🌟 Manager

Im not sure any 10% rule applies to safflorites, but does for some pyroxenes; but the whole Ca-Fe-Mg pyroxene system is a lot more complex than shown on this diagram. Eg. See https://journals.lib.unb.ca/index.php/GC/rt/printerFriendly/2696/3123, fig. 7. We should also show the miscibility gap between augite and pigeonite and Opx, shown in the same figure, though it varies with T and P. There are some good pyroxene figures in https://www.slideshare.net/mobile/joqwerty/pyroxenes-pdf.

Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: April 25, 2024 20:14:58

Go to top of page