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When can a fossil be also considered a mineral?
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Ru Smith




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PostPosted: May 14, 2013 19:57    Post subject: Re: When can a fossil be also considered a mineral?  

That is a fascinating coral enclosed in hematite, Philip. Brian Young has a paper in the Journal of the Russell Society (2012) which shows a colonial coral (?Siphonodendron sp.) preserved in hematite from the old Florence Mine dump. "The skeletal elements of the original coral are preserved in quartz surrounded by massive hematite."

My favourite example of mineralization of fossils is the replication of soft parts by very early precipitation of pyrite, such as is seen in the Ordovician of New York or the Devonian of Bundenbach in Germany.



Bunden 12.jpg
 Description:
Mimetaster hexagonalis, Lower Devonian, preserved in early-precipitated pyrite.
Bundenbach, Germany.
35 mm in ventral view on slab with ophiuroid. Published in Hohenstein (2004), BJR 77, 420-425, Fig. 4.
 Viewed:  17944 Time(s)

Bunden 12.jpg


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PostPosted: May 15, 2013 07:36    Post subject: Re: When can a fossil be also considered a mineral?  

alfredo wrote:
Fossils could be divided into two types:

1) The dead organism's original organic material is preserved without replacement, as for example with Siberian mammoths frozen for 20,000 years, or giant ground sloths merely desiccated in dry caves, or human beings pickled in the acid waters of peat bogs. These fossils are NOT minerals, obviously.

2) The much more common type of fossil in which the original organic matter is replaced by mineral matter. These are obviously both fossils and minerals, and any distinction is merely semantic and due to the collection preferences of the person who has it. I'm sure most MINERAL collectors would not consider a fossil to be a mineral SPECIMEN unless it contained either visible crystals or some interesting replacement species (opal, vivianite, etc). A fossil composed of clay minerals is of course also a mineral, but few mineral collectors would consider it to be a mineral "specimen".


Hi to everybody!
According to the definitions of Hugo Strunz, even a shell or a bone (including human bones) are to be considered minerals. From my personal point of view (it's just an opinion, don't misunderstand me!), I don't agree. A fossil IS a plant or animal rest or trace which WAS transformed into mineral or minerals by the time. This definition doesn't exclude the single pyrite crystal forming an ammonite IS a pyrite crystal, or the single quartz crystal forming a fossil shell IS a quartz crystal. Living shells and bones are NOT separate mineral species, but they are a mixture of EXISTING and CLASSIFIED mineral species (aragonite for shells and apatite for bones), and organic substances. The latter ones allow shells and bones to be "alive" structures of an organism. I hope I was clear enough.
Greetings from Italy by Riccardo.

The definitions of "mineral" and "fossil" are pretty well established and it would be redundant to rehash them here, so what this discussion is really about is the definition of "specimen"!

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Hi! I'm a collector of minerals since 1973 and a gemmologist. On Summer I always visit mines and quarries all over Europe looking for minerals! Ok, there is time to tell you much much more! Greetings from Italy by Riccardo.
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PostPosted: May 16, 2013 17:34    Post subject: Re: When can a fossil be also considered a mineral?  

Carles Millan wrote:
Don Lum wrote:
I don't know if there are any wiser people on the Forum than you, Carles.

By the hundreds !

Carles, I think that the software we all enjoy on The FMF (Freeware: Mineral Database ) looks like the work of a genius.

Sincerely,

Don

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PostPosted: May 16, 2013 18:46    Post subject: Re: When can a fossil be also considered a mineral?  

Carles Millan wrote:
In https://www.mineral-forum.com/message-board/viewtopic.php?p=31223#31223 Don Lum wrote:
Opal var Shell Opal
Belemnite

From that post an interesting question arises. When can a fossil be also considered a mineral?


Hi Carles,

I found some information that you might find interesting.

Excerpt from raysrockandminerals:

FLORIDA AGATIZED CORAL



In 1979 the State of Florida designated Agatized Coral as its state stone (although it’s actually a fossil…). Coral falls into the marine animal class of Anthazoa. These living polyps secrete calcium carbonate to form tropical ocean reef systems. Agatized coral occurs in one of three ways: Silica will replace a portion of the coral, creating geodes, sometimes with brilliant quartz crystal clusters inside. These crystals are very small. They are commonly referred to as druzy quartz. Sometimes they are replaced with botryoidal (grape like) quartz formations. In extremely rare instances water will become trapped inside the geode. These are called enhydros. In the second occurrence, the Coral is completely replaced by silica creating some exotic specimens. A third way is when the coral is trapped in lime stone and is slowly dissolved, leaving a perfect cast. Then silica seeps into the cavity duplicating the coral in silica. This is called a pseudomorph (one mineral replacing another). Although it doesn’t sound like a drawn out process, it is. It takes about 20-30 million years for this to happen.

In Florida, agatized coral is found in three main locations: (1) Tampa Bay around Ballast Point (2) the Ecofina River in the panhandle approximately 15 miles west of Perry, Florida off US 98, and (3) the Withlacoochee/Suwannee river beds.

Georgia shares the Withlacoochee River with Florida. Near Clyatteville, Georgia this river flows over an ancient coral reef from the Oligocene Epoch which began about 38 million years ago and lasted for approximately 11 million years. These ancient coral reefs become exposed in river beds which, over time, erode and cut valleys through sediment exposing the coral.

Agatized coral is found in a variety of colors. The color depends largely upon the minerals present in the silica when the process was taking place. The colors are typically gray, brown, honey and white, but they are also found in red, black, orange and sometimes blue. Geodes found in these areas of Florida and Georgia can be melon size or even pumpkin size if you are lucky.

The beautiful specimens of agatized coral that occur at Ballast Point area in Tampa Bay have been known since the late 19th century. These specimens are actually chalcedony pseudomorphs after coral or aragonite (the mineral which made up the original coral skeletons). The exterior details of the specimens from this and other locations are often preserved in exquisite detail, thanks to the silicification process. However, interior details of the original coral skeleton are often obscured in geodes, replaced by chalcedony.

Agatized and silicified corals are largely associated with Tertiary marine sedimentary formations from the eastern Florida panhandle and nearby south Georgia through central and west Florida, as far south as Sarasota County. Calcified corals have been found in several southern Florida localities. Most of the major deposits seem to occur in upper Oligocene and lower Miocene shallow marine limestone and marls.

So if the State of Florida recognizes fossilized agate as The State Stone, then maybe it is a stone :-).

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PostPosted: May 17, 2013 04:53    Post subject: Re: When can a fossil be also considered a mineral?  

Don Lum wrote:
Carles Millan wrote:
Don Lum wrote:
I don't know if there are any wiser people on the Forum than you, Carles.

By the hundreds !

Carles, I think that the software we all enjoy on The FMF (Freeware: Mineral Database ) looks like the work of a genius.

I'm very glad that the software can be useful for somebody.
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PostPosted: May 17, 2013 05:02    Post subject: Re: When can a fossil be also considered a mineral?  

Don Lum wrote:
So if the State of Florida recognizes fossilized agate as The State Stone, then maybe it is a stone :-).

The US Supreme Court unanimously decided long ago (year 1893) that tomatoes were NOT a fruit but a vegetable.
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PostPosted: May 17, 2013 09:40    Post subject: Re: When can a fossil be also considered a mineral?  

Carles Millan wrote:
Don Lum wrote:
So if the State of Florida recognizes fossilized agate as The State Stone, then maybe it is a stone :-).

The US Supreme Court unanimously decided long ago (year 1893) that tomatoes were NOT a fruit but a vegetable.


So, what does the 'supreme court' of Carlos say, is it a stone or not? :-)

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PostPosted: May 17, 2013 10:56    Post subject: Re: When can a fossil be also considered a mineral?  

Hello,
Without giving a lesson, I think fossilization is actually a pseudomorphosis whose shell (for example) gives the form.
A conventional mineral pseudomorphosis is the gradual transformation of azurite into malachite. The material turns without transport. The resulting crystal of malachite retains the shape of the initial azurite. But malachite is not a single crystal.
A fossil is a residue of an organic, a plant or animal skeleton. Silica impregnated wood fibers whose soft material disappears.
A shell will fill with sediment, calcite, pyrite, etc…
In general, a fossil will be a differentiated rock or a mineral depending on the composition.
I'll post another interesting topic, I think.
Roger.
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PostPosted: May 17, 2013 11:21    Post subject: Re: When can a fossil be also considered a mineral?  

Hi,
At the 2002 Munich Show, my friend Roger Titeux asked me to buy two fossil specimens. I refused for lack of money. But I regret it now, and for a good reason.
Both fossils were made of emerald. I think the emerald has replaced the calcite filling the shell, in a flow of hydrothermal waters.
These fossils come from the famous Valley of Colombia, and I think remember from Gachala.
I think in this case, we can say that the fossil is a mineral.
Here are the photos.
Roger.



Fossile-1-2284_R.jpg
 Description:
Emerald - fossil
Colombia, Gabachla ?
3-4 cm
 Viewed:  17751 Time(s)

Fossile-1-2284_R.jpg



Fossile2_2286_R.jpg
 Description:
Fossil - emerald
Colombia, Gabachla ?
3-4 cm
 Viewed:  17600 Time(s)

Fossile2_2286_R.jpg


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PostPosted: May 17, 2013 11:41    Post subject: Re: When can a fossil be also considered a mineral?  

Roger,

That is an amazing specimen and great photos. Thank you.

Don

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PostPosted: May 17, 2013 13:59    Post subject: Re: When can a fossil be also considered a mineral?  

Roger Warin wrote:
Without giving a lesson, I think fossilization is actually a pseudomorphosis whose shell (for example) gives the form. A conventional mineral pseudomorphosis is the gradual transformation of azurite into malachite. The material turns without transport. The resulting crystal of malachite retains the shape of the initial azurite. But malachite is not a single crystal. A fossil is a residue of an organic, a plant or animal skeleton. Silica impregnated wood fibers whose soft material disappears. A shell will fill with sediment, calcite, pyrite, etc… In general, a fossil will be a differentiated rock or a mineral depending on the composition.

Indeed it's been an excellent lesson, Roger. A splendid explanation we should take good note of.

Thank you!
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PostPosted: May 17, 2013 14:51    Post subject: Re: When can a fossil be also considered a mineral?  

A cautionary note:

The use of term pseudomorphosis to define the replacement of a mineral after a biological remain, even if the remains are of inorganic nature (as bones or shells) is a misuse. The substitution of a biomineral or an organic structure by a new mineral (silica after phosphate or after wood's lignin) is a replacement, not a pseudomorphosis. The pseudomorphosis refers to the maintaining of the crystal shape of an euhedral or idiomorph original crystal. I remark, crystal shape. Again (maybe the words of the south europeans are worth less), the sentence "pyrite after ammonite" suggesting a pseudomorphosis is not correct and should not be used in labels.
Although from an etymological view, pseudomorphosis could refer to any replacement that maintain the former shape, from a mineralogical view, the use of pseudomorph is clearly defined and not mixed with fossilization or replacement terms. Replacement is the general term that encompass the other and, in doubt, it should be used.
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PostPosted: May 17, 2013 16:00    Post subject: Re: When can a fossil be also considered a mineral?  

Hi,
Your point is well taken. But as long ago as I left the academic way, which makes me also to address a literary public by taking some liberties with the specific discipline. So I chose to use the term "pseudomorphosis" according to the Greek signification. Roger Titeux’s emerald has the form of a shell, but it is not. This is obviously a crystallographic impossible because even the helicity of the shell is respected (dextrorotatory or screw right).
Excuse my reply, but I do not think anyone knows the sequence of processes that led to the formation of this beryl, apart from the general context of a hydrothermal type. The "replacement" is certainly not trivial.
Roger.
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PostPosted: May 17, 2013 16:54    Post subject: Re: When can a fossil be also considered a mineral?  

Hi Roger,

Indeed, the beryl fossilized gastropods from Gachala are very interesting. I'm not expert in these deposits, but to my eyes are not very surprising taking into account that the hydrothermalism of these deposits is epigenetic and the deposit is associated to marine black shales. The metasomatism of organic rich black shales, with presence of macrofossils, by hydrothermal fluids could explain the replacement of the original material of gastropod by beryl. I think that, in this case, the major mystery is not the "berylized" fossils, that, to my eyes appears as an usual replacement (in this case, beryl instead of a more common silica, after carbonate? or after previously silicified remains, that could explain that the original shape survived the hydrothermalism with only partial dissolution?). More difficult to explain is the origin of a remarkable beryllium anomaly.

As I said I'm not expert in these deposits and this is a mere 'back envelope' hypothesis and I should revise all published references. Anyway, as you said is not trivial, but still I wouldn't define these "emerald snails" as a case of pseudomorphosis. I hope that an expert in the Gachala and related deposits read my brief explanation and can elaborate it.
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PostPosted: May 17, 2013 18:58    Post subject: Re: When can a fossil be also considered a mineral?  

Carles Millan wrote:
Don Lum wrote:
So if the State of Florida recognizes fossilized agate as The State Stone, then maybe it is a stone :-).

The US Supreme Court unanimously decided long ago (year 1893) that tomatoes were NOT a fruit but a vegetable.


I agree with the U.S. Supreme Court on that one. I think that tomatoes are vegetables. But I give you the last word. Or did I just get the last word?

Don

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PostPosted: May 18, 2013 02:01    Post subject: Re: When can a fossil be also considered a mineral?  

The process of fossilization involves the substitution molecule by molecule of most of the original animal compounds. In this sense, fossilization is, at the same time, a mineralization.
But, must we include fossils in mineral collections? I think the answer is yes and it is not (in another word: it depends!).

Would you include a calcitic ammonite in your collection? Surely no.

But, and this (see the picture)?

It is a silicified (chalcedony) Pleurotomaria sp., from Germany.



quars_cl_1965_10br.jpg
 Description:
Quartz (chalcedony)
Kapellenberg, Sachsen, Germany.
3,5 x 3,9 x 1,6 cm
Botryoidal growths.
 Viewed:  17354 Time(s)

quars_cl_1965_10br.jpg


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PostPosted: May 18, 2013 02:10    Post subject: Re: When can a fossil be also considered a mineral?  

By other hand, fossils are present as a base for finely recrystallized minerals (i.e. some phosphates as apatite, vivianite or anapaite, carbonates as calcite and aragonite, oxides and hydroxides, as goethite, or sulphides as pyrite and marcasite).

See the picture of this anapaite from Crimea (Krim), the base of the crystals is a valve of a fossil bivalve shell, not easaily visible on the photo, but it is complete.



anapaita_1992_29br.jpg
 Description:
Anapaite
Kerč, Peninsula of Krim (Crimea), Ucrania.
3,4 x 2,2 x 0,8 cm.
 Viewed:  17401 Time(s)

anapaita_1992_29br.jpg


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PostPosted: May 18, 2013 03:53    Post subject: Re: When can a fossil be also considered a mineral?  

Don Lum wrote:
Carles Millan wrote:
Don Lum wrote:
So if the State of Florida recognizes fossilized agate as The State Stone, then maybe it is a stone :-).
The US Supreme Court unanimously decided long ago (year 1893) that tomatoes were NOT a fruit but a vegetable.
I agree with the U.S. Supreme Court on that one. I think that tomatoes are vegetables. But I give you the last word. Or did I just get the last word?

I'm not going to keep this off topic controversy alive, so here are my last words about it:

If the tomato vegetable is not a fruit, then can you please tell me what the fruit of the tomato plant is? You may want to clear your doubts on Wikipedia rather than on the year 1893 (I believe) flawed US Supreme Court sentence.
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PostPosted: May 18, 2013 04:14    Post subject: Re: When can a fossil be also considered a mineral?  

Hi Cesar,
Thank you for your very nuanced reply. I think with you it was good to stay rigorous even for the general public. But the scientific popularization is a difficult art.
Roger.
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PostPosted: May 18, 2013 13:02    Post subject: Re: When can a fossil be also considered a mineral?  

US Supreme Court are not botanists (evidently).
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