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Crinoid-limestone, Calcite : CaCO3

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Copyright © Bill Cordua
 
 
 
 
minID: UU0-XWV

Crinoid-limestone, Calcite : CaCO3

Copyright © Bill Cordua  - This image is copyrighted. Unauthorized reproduction prohibited.
Dimensions: 13 cm x 8 cm
Field of View: 15 cm

Calcite as limestone and fossils in "crinoid pizza" from the Stobo bioherm. Scale is in centimeters.

This photo has been shown 384 times
Photo added:8th Nov 2013
Dimensions:1280x960px (1.23 megapixels)
Camera:NIKON E995

Data Identifiers

Mindat Photo ID:570594 📋 (quote this with any query about this photo)
Long-form Identifier:mindat:1:4:570594:5 📋
GUID:a881e703-36d8-4c73-86c3-97fe2aabde12 📋
Specimen MinIDUU0-XWV (note: this is not unique to this photo, it is unique to the specimen)

Discuss this Photo

PhotosWould anyone consider this "calcite"?

15th Oct 2020 04:52 UTCBob Harman

Fossiliferous limestone with numerous broken segments of crinoid stems, but no "calcite"......or does anyone consider a specimen like this"calcite"?       BOB

15th Oct 2020 05:18 UTCRichard Gibson 🌟

Well, the only mineral you would find in that, by x-ray diffraction or any other test, is calcite.

15th Oct 2020 08:42 UTCErik Vercammen Expert

It is a pseudomorph of calcite after crinoids.

15th Oct 2020 09:05 UTCAlfredo Petrov Manager

I agree with Richard and Erik that yes, it is a calcite specimen. If one were building a comprehensive calcite collection (perish the thought) and wanted calcite with as many different forms and localities as possible, this one would certainly have a place in the collection.

15th Oct 2020 09:34 UTCErik Vercammen Expert

This is an example of the discussion how a collection of a mineral should be: just "average" = common specimens, or only bling bling? I think that in a calcite collection, you should have a piece like this one,  a fossil with crystals in cavities, and a chunk of limestone, marl and marble. And in a collection of an "ore mineral" like galena or chalcopyrite, there should be also a specimen of "commercial" ore (likely an "ugglity"!)

15th Oct 2020 10:05 UTCPaul De Bondt Manager

Keep in mind that such specimen exist in Beez quarry, rare not that rich off course, and they are dolomite.

Keep safe.

18th Oct 2020 02:37 UTCDoug Daniels

To me, looks like an awful lot of crinoid fragments.  As I remember, each segment of the crinoid stem is actually a single calcite crystal (look at a section under a polarizing microscope).  So, guess it is basically a calcite specimen, even though more properly a fossil.   To each his/her  own.

19th Oct 2020 03:04 UTCGregg Little 🌟

To answer the original question, I see no problem calling this specimen calcite as that is the dominant mineral present.  My only concern is that there should be an added description that the calcite originated as a crinoidal limestone deposit.  Leaving it as calcite is incomplete possibly leading to the assumption that the calcite of this form was deposited by an inorganic process.  This may have been alluded to by "(Stobo bioherm)" in the description, but this may not necessarily be clear. 

A similar point can be made about dolomite in sedimentary basins. The term dolomite and dolostone is interchangeable but most dolomite is secondary and so is essentially a monomineralic rock formed by metasomatic processes.  Another similar case is gypsum where sedimentary beds of gypsum are mostly referred to as gypsum and infrequently as an evaporite rock.

19th Oct 2020 04:32 UTCMark Heintzelman 🌟 Expert

02909610016030782576510.jpg
There are some examples of fossilization/replacement I would regard as reasonably labeled Calcite and others, like that limestone feature above, that I personally would regard as stretching the definition a bit far. As an example, I would be fine with these Belemnite replaced by a relatively pure calcite, which even retain a certain translucency.

Last time I looked, Limestone (which is what that is) was regarded as a type of rock, not a mineral.  Is this really a delineation we should intentionally blur, or one that need not exist?

19th Oct 2020 09:30 UTCPaul De Bondt Manager

Since we may upload fossils now on Mindat, I would change it to " crinoid ".
That would resolve the question and could be documented in the text.

Keep safe.
 
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