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Radiolarite, Chert, Quartz : SiO2
Lautenthal, Langelsheim, Goslar District, Lower Saxony, Germany

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Copyright © Amir Akhavan
 
 
 
 
minID: U66-EKG

Radiolarite, Chert, Quartz : SiO2

Copyright © Amir Akhavan  - This image is copyrighted. Unauthorized reproduction prohibited.
Locality: Lautenthal, Langelsheim, Goslar District, Lower Saxony, Germany
Dimensions: 80 mm x 50 mm x 34 mm

A piece of radiolarite from an old quarry in Lower Carboniferous rocks on the eastern bank of the Innerste river, immediately north of Lautenthal. This chert is composed mainly of microcrystalline quartz, not unlike flint, but has formed by compaction and recrystallization of deap sea sediments primarily made of the opaline tests of radiolaria, single cell protozoa. The folding of the rock body led to the formation of a lot of small and often straight quartz veins that run criss-cross through the rock.

Size of specimen 80 x 50 x 34 mm.


This photo has been shown 6283 times
Photo added:7th Sep 2014
Dimensions:7616x5408px (41.19 megapixels)

Data Identifiers

Mindat Photo ID:635165 📋 (quote this with any query about this photo)
Long-form Identifier:mindat:1:4:635165:3 📋
GUID:f1373a65-6b50-4171-9f41-aa34aa49adb9 📋
Specimen MinIDU66-EKG (note: this is not unique to this photo, it is unique to the specimen)

Discuss this Photo

Photosradiolarite vs. chert - or maybe lydite?

17th Feb 2022 21:05 UTCKrzysztof Andrzejewski

This kind of rock as I know was always called Lydite. Mindat definition treat it as synonime of radiolarite. But as I remember, the black color of lydite due to the content of organic substances meant that the highest-quality lydite were used to determine the purity of gold by scratching a streak and comparing the color. On the other hand, a comparison with chert - it is a completely different type of sedimentary environment, a different facies: here deep see and on the other hand, shallow condition for chert. Treating radiolarite = chert names as an alternate is wrong. But my memory is not that good as it use to be, maybe some geologists will comment? greetings

17th Feb 2022 21:39 UTCAmir C. Akhavan Expert

This can be called lydite, too.
A very common term in the sedimentological literature is "radiolarian chert", that would be another option. About chert:
The rock corresponds to what is written there ("bedded chert"). In thin sections of this rock one can see remnants of radiolarian tests.
I've called it chert to clearly distinguish it from the phantasy rock "radiolarite" as defined in the BGS.

17th Feb 2022 21:43 UTCKrzysztof Andrzejewski

chert could be easily associated with limestones but this is opposite to black Lydite facies of deep sea

 

17th Feb 2022 21:55 UTCAmir C. Akhavan Expert

The definitions are about the rocks themselves, not their associations, so when you hold a rock in your hand you can tell what it is.


18th Feb 2022 16:42 UTCKrzysztof Andrzejewski

I mostly never try to say what is this - regarding rocks. I'm trying always to say what could be done to be sure, what is this. And regarding to the chert - compare matrix of Tri-State Mining District specimens to this photo...

19th Feb 2022 22:30 UTCKevin Conroy Manager

Krzysztof Andrzejewski 🌟   ✉️

chert - compare matrix of Tri-State Mining District specimens
 

For the record, some dark colored matrix was found in portions of Cherokee County, Kansas.   It made for attractive specimens when quartz crystals grew on it.

18th Feb 2022 01:20 UTCPavel Kartashov Manager

From my point of view radiolarite must to be composed mainly by radiolaria skeletons. Chert may to contain such skeletons, but in subordinate quantities, because it forms during solidification of silica gels. A source of such gels may to be of different origin, in that number hydratation of radiolaria skeletons.
In any case, if you speak about radiolarite, you must to demonstrate thin section overfilled with radiolaria skeletons or at least by its abundant fragments.

18th Feb 2022 21:44 UTCRalph S Bottrill 🌟 Manager

Cherts can form in numerous ways, some as nodules in limestone, some by alteration of radiolaria, some as hydrothermal exhalation deposits or replacements. It can be hard to tell without thin section petrology etc.

18th Feb 2022 21:48 UTCKrzysztof Andrzejewski

Ralph - if I remember, over 4 km deep no chance for limestone sedimentation in the oceans, but perfect for such rock as this one on the photo

19th Feb 2022 00:00 UTCMaxwell Hain

https://geo.libretexts.org/Bookshelves/Oceanography/Oceanography_101_(Miracosta)/06%3A_Marine_Sediments/6.21%3A_Calcium_Carbonate_Compensation_Depth_(CCD)

Kind of splitting hairs now, but you did point out a common issue with names and how they are applied depending on context can mean something different. Agree with Ralph, a thin section would be needed to make that distinction, until then its just called a chert.

18th Feb 2022 22:17 UTCRalph S Bottrill 🌟 Manager

I’m not sure where limestones come into this? As I say not all cherts occur in limestone.
I think Lydite is usually defined as a black, carbonaceous variety of a radiolarian chert, not a synonym of radiolarite, though I have seen it described in some dictionaries as a basaltic rock. (Basanite can be a synonym of lydite or a basaltic rock). I will try to tidy up the nomenclature and structure here a bit.

19th Feb 2022 04:58 UTCRalph S Bottrill 🌟 Manager

I have had a start a tidying up touchstones, Lydite, the bio-siliceous earths, oozes and rocks:

19th Feb 2022 07:18 UTCKrzysztof Andrzejewski

I checked what the Wiki says about it, and I think that the introduction of mass use of the term 'chert' is another effect of Americanization in geology.

19th Feb 2022 11:03 UTCAmir C. Akhavan Expert

Ralph, the hierarchical presentation of siliceous ooze and earths is problematic (I know you have not created the hierarchy).
It includes biogenic and "chemical" species in the description, but only lists biogenic ones as "subdivisions".
I have never seen or heard of chemical silica ooze, so I can't say anything about its composition. To my knowledge, lab-grown silica ooze would all be opal-AG.
Are there samples of chemical silica ooze?

Anyway, the "Mineralogy" sections of the biogenic ones are misleading. They list
opal-A, opal-C, opal-CT and quartz as "non-essential minerals" that are "common, sometimes major components, but are not always present".
If present, opal-C, -CT, -AN, and quartz have been added as a sediment, just like dead fish. A potential source would be volcanic ash, for example.
I strongly recommend to leave non-essential minerals out.

On the other hand, essential minerals are missing. That might be because of a traditionalist approach that excludes anything non-geological. Whatever the reasoning behind this, if there was a reasonging behind it, listing biogenic opal as the essential component is important.
Also, material that is predominantly made of diatoms/radiolaria/spicules cannot possibly have opal-C, opal-CT or quartz as "sometimes major components". Unless imported from other sources as additional sediment (like dead fish, as mentioned above), these components will only form during diagenesis, when the ooze has long been compacted into a solid rock.

Probably biogenic opal is structurally not related to either opal-AG and opal-AN, as the silica tests are fabricated by special enzymes, and diatoms, radiolaria and sponges use different enzymes for this. It is amorphous opal, though, no cristobalite or tridymite in it. 

I do not like the term "silicified radiolarite", as it sounds like a replacement by and consequently enrichment in silica. All that happens during diagenesis is recrystallization of already present biogenic silica into quartz (with cristobalite/tridymite as intermediate steps). So if at all, it is "quartzified".

The biggest problem to me is this:
While the older chert page lists examples and lots of references, the new predefined hierarchical entries have none.
We take the hierarchical entries as gospel and try to talk sense into them. Whenever our exegesis fails and we are at a loss, we cite Wikipedia. Which really is a shame.

20th Feb 2022 00:18 UTCKeith Compton 🌟 Manager

And of course Wiki is only as good as the information that has been uploaded voluntarily. The uploaders of course are also not necessarily experts.
Mistakes are made, changes made that may or may not be correct and the information is constantly evolving.

Not saying Wiki is wrong ... just saying

19th Feb 2022 14:08 UTCRalph S Bottrill 🌟 Manager

Hi Krzysztof
You are probably correct that chert has lost its original meaning but that’s what happens with time and distance to many words. So we really need to include all the different current usages for readers, just as we say that basanite can be used for a basaltic rock as well as a cherty rock. I guess we could try to emphasise the original use of the word, if not entirely lost to history?

Amir, yes I’m not completely sure where all the hierarchies came from (though in large part the BGS classifications) or the mineralogies. I originally tried to help with some parts, mostly igneous, but it all happened fairly quickly and I’m really not expert on all rocks, sediments, etc. So now I just try to fix really dodgy bits of structure, definitions etc. as I come across them, based on various texts and Wikipedia. Even the latter is dodgy in parts! I agree we need more reference, I admit to doing a lot of definitions etc from memory, thinking I will add the refs later.

So far with these siliceous rocks I pulled them out from under clays and tried to give more logical structures. Hopefully clarified the Lydite/basanite/touchstone/radiolarite relations. Tried to put the various oozes and earths together ind indicate links and relations to the siliceous rocks.  Moved touchstone to the glossary as it’s really not a rock type but a manufactured object class like a building stone etc. 

I haven’t really thought about mineralogies yet but agree this needs some work. Sometimes non-essential minerals are useful, eg in igneous rocks, but not so sure with sediments.  We do have abiogenic silica as sinter and geyserite, not sure about the oozes but I understand they must occur in siliceous iron formations etc? I’m not sure we have biogenic silica in Mindat but I take your point it’s probably different enough from other forms of opal to justify, though perhaps we should do the same with biogenic apatite, calcite, aragonite etc? These things tend to be composite organic-mineral composites.

 I don’t know where you found silicified radiolarite but i agree it’s misleading terminology, though I understand these materials evolve from biogenic silica through to quartz by sequences of diagenetic dissolution and reprecipitation, gradually filling voids? 

Anyway, Amir, I am happy for you to work on any areas of this you wish, I just tried to fix the most glaring errors I could see at a glance.


19th Feb 2022 15:23 UTCAmir C. Akhavan Expert

>  but I understand they must occur in siliceous iron formations etc?
Ah, good example. Now we only need some real material from 2022 ;-)

> Anyway, Amir, I am happy for you to work on any areas of this you wish, I just tried to fix the most glaring errors I could see at a glance.
You probably know my answer. It is a lot of work with endless discussions, and
when the BGS-based hierarchy appeared, I got frustrated, stopped working on rocks and switched to a "lazy complain mode".
I'm happy to change terminology and names, as long as it is somewhat consistent. But I'd rather wait until some IUGS commission publishes something to refer to, and not touch or work on the rock hierarchy as it is now (I wouldn't even know how).

I can add some text to the siliceous rocks/earths/oozes that explains their mineralogy and formation etc. with references.

Biogenic opal... a few years ago I tried to figure out what it is "mineralogically", but couldn't.
Those who study spicules and tests live in a happier world: they simply don't care whether it is opal-A or not :-)

"silicified radiolarite" is used on the lydite page.


((( "Lydite is the mineralogicalification of lydia stone (touchstone)" OMG, a long English word )))

19th Feb 2022 19:29 UTCKrzysztof Andrzejewski

I have to say something  - I really don't know much about 'chert' and honestly, don't want to know more than necessary. I started this topic because I believe that regardless of new ideas and changes in the nomenclature, what's old doesn't have to be bad at all, especially if it's been working great so far. 
From German Wiki:
'Paleozoic dark radiolarites are also referred to as Lydite or Kieselschiefer, although they are often not slatey.'

Polish Wiki:
'Lidite - sedimentary silica rock belonging to the group of organogenic rocks, black or dark gray, cryptocrystalline or very fine crystalline. It consists mainly of chalcedony and microcrystalline quartz and organic substances, and often pyrite. The content of clay minerals and pyroclastic components causes layering. During diagenesis, as a result of chalcedony recrystallization, quartz veins cutting through the rock in different directions are formed. The organic substance found in the lidites is a highly carbonized.'

It's more or less like the term 'jasper' - which I stopped using completely, because everybody have own idea about what this goddamn jasper is. It can be silicified sedimentary rock as a result of contact with volcanic lava, or a purely hydrothermal mix of minerals in the voids of the lavas. Who cares in the internet era? Whatever the scientific definition and terminology is, has totally lost its relevance...

20th Feb 2022 14:58 UTCRalph S Bottrill 🌟 Manager

Hi Krzysztof
I’m happy to have old definitions but Wiki descriptions are  not old and as Keith noted above no always accurate and we would prefer formal published references. Of course most of our rocks have no references; I think Jolyon hoped we would rush to do these once he added the rock names, but who has time? Nevertheless I added a better description for Lydite, if you or anyone has original references I’m happy to add them, but haven’t found much yet. 

I do agree jasper has almost become a meaningless term, it’s been Lapidarificationed or some such corruption!

20th Feb 2022 15:12 UTCRalph S Bottrill 🌟 Manager

Hi Amir
I have also been waiting decades for the IUGS to continue sorting rock names, but I really don’t think anything is happening. Maybe too many arguments with the early versions? So I just try to use some common sense and 40 yrs of experience, (possibly the same thing?) and tweak a few bits here and there and hope it helps. 

I amended the silicified radiolarite on the Lydite page, though I think maybe it alluded to the fact the material commonly contains quartz in veins and filling pores, like a silicified sandstone.?

I’m aware you are busy but am sure anything you add will be much appreciated, especially with references.


20th Feb 2022 18:28 UTCAmir C. Akhavan Expert

Instead of chasing and fixing new entries in the ever-branching sedimentary rock "tree" it might be better to write a single brief overview article and put a link to it on the different pages. But if I will ever find the time to work on it...

At least, I can give you one funny reference for chemically precipitated siliceous ooze:
Gómez, J., Gil, M.L.A., de la Rosa-Fox, N., Alguacil, M. (2015) Formation of siliceous sediments in brandy after diatomite filtration. Food Chemistry: 170: 84-89.
Cheers!

20th Feb 2022 21:14 UTCRalph S Bottrill 🌟 Manager

That sounds useful thanks Amir, and the article sounds a good one to read with an after-dinner drink!

20th Feb 2022 22:04 UTCKrzysztof Andrzejewski

German Wiki most important reference:
Dorrik A.V. Stow (2008) Sedimentgesteine im Gelände. Ein illustrierter Leitfaden. Spektrum Akademischer Verlag, Heidelberg   
Polish Wiki:
Ryka W., Maliszewska A. (1982), Słownik petrograficzny, Wydawnictwa Geologiczne, 
Warszawa
- but it doesn't really matter. For hundreds of years we had the Zn/Pb Germanic Trias type deposit and now it turned out that it is not true because the only right is MVT-type. Hundreds of years of exploring the geology of Carboniferous and finally system was separated by Conybeare & Phillips in 1822 on the basis of studies of sediments in England and Wales, later with addition of studies from Belgium, France or Germany and?? No more Namurian or Westphalian - for Mindat only Mississippian and Pennsylvanian... 
Majority of mines long time closed, so it's not really matters, so let's make now 'chertisation' everywhere, who really cares? 


 
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