FMF - Friends of Minerals Forum, discussion and message board

[Bob Harman]

A very old thread is resurrected. A nice example of what Steve was referring to in his last post of 2013.

Quartz replacing a fossil brachiopod from Monroe County Indiana.
This is the rare "dewdrop diamond" variant as individual smoky quartz crystals
sparkle like dewdrops in bright sunlight. Bob

[David K. Joyce]

Here is a mineral specimen disguised as a fossil. A gastropod, I think. It is as thin as an eggshell and totally composed of tiny calcite or dolomite crystals.

[Scot Krueger]

I had to ask myself the question many times when I decided to finally create a formal catalog of my collection. Since I have collected both fossils and minerals my whole life, I have many of both. So it was natural to create a flag in the database to declare whether a sample was a "fossil" or a "mineral" (or a rock, or jewelry, etc.). But I found there were a handful of examples that could easily fit either category. The attached photo is one such example. It is a fossil clam from Florida which is lined with beautiful golden calcite crystals. I finally decided the question by asking myself, if I had to house my fossils and my minerals in different buildings, which building would I put this in? Since I had bought it at the Tucson Gem and Mineral Show because I loved the golden calcites, I decided this one was a mineral specimen. But I have other, self-collected fossils which have calcites in the void space that are far from aesthetic enough to raise the question, and those I kept primarily as fossils, so they got the fossil tag.

[R Saunders]

Mercernaria sp. means edible Mollusk. Former Ruck's itt quarry, now closed to collecting.

[Bob Harman]

Scott's example and R Saunder's examples are minerals associated with fossils.

Calcite crystals associated with clam shell fossils from Ruck's pit in Florida.
Mine and David J's are quartz or calcite replacing the fossil.

The association of the 2 or the replacement by one of the other are 2 very different processes.

The original posting was what to call the example: fossil or mineral.
With the association of the 2, there is both a mineral and the fossil, not one or the other. Bob

[R Saunders]

[marco campos-venuti]

I am reopening this interesting topic because I came across a bivalve in fluorite from Belgium that seems very unique to me as it appears to be made of monocrystalline fluorite.
I find the discussion very interesting, but it seems to me to see a group of cats marking territory. The fields of science overlap and it is not necessary to claim the property. Paleontologists and mineralogists can coexist and study the same things, without quarreling.
All fossils are made of minerals as minerals constitute all rocks and fossils are the remains of petrified animals. Furthermore, many minerals are the result of biomineralization, that is, their precipitation is induced by biological activity.
Biomineralization can be Biologically Controlled Mineralization (BCM) like a skeleton or Biologically Induced Mineralization (BIM) like a stromatolite. In the first case the characters evolve because they are controlled by genes, in the second there is no evolution because the shape is controlled by the environment and in fact living stromatolites are identical to those of the Dresser Formation dated to 3.47 By.
So the question should be when can I introduce a fossil into a mineral collection? And the obvious answer is: whenever you want, the collection is yours. An internal cast of a gastropod in emerald or the external cast of a bivalve in fluorite is a fossil and should be exhibited in a fossil collection, but you can also put it in a collection of minerals, or shells or naturalistic curiosities!!
It is curious how sciences that are exact in their most evolved expressions, are often extremely inaccurate in their original definitions. In fact it is very difficult to define something before knowing it and when you know it the definition is of little use. It is more a debate in the philosophy of science.
In biology the definition of species is still unclear, defined as a classification category of organisms that includes individuals capable of mating with each other and generating fertile offspring, but if I lock a lioness and a tiger in a cage, the perfectly fertile tigons come out. Even the definition of life is unclear, viruses are still not considered living beings, but can kill us.
In mineralogy the same thing happens, the rush to mark territory has created pseudofossils and mineraloids, two absolutely useless and decidedly unclear categories. Even the so-called molecular fossils cited by Cesar are nothing more than organic compounds that end in -ite. Organic chemistry includes all carbon compounds except oxides. Organic compounds in general have a polymeric structure, but also certain minerals, such as silica polymers, that is, the microcrystalline varieties of silica, opal, jasper and chalcedony, unrecognized species, but which on numerous occasions I have demonstrated to have an important mineralogical individuality.
In this regard, I recall that among tourmalines it is possible to have two distinct minerals with the same composition, only by moving an ion from one position to another. And today we have 41 tourmalines, which few peoples in the world are able to distinguish with sophisticated analysis. On the contrary, the hydrated phases of quartz, jasper and chalcedony are considered as varieties of quartz. So why are gypsum and anhydrite two different minerals? Opal is a mineral species only for historical reasons even though it is amorphous, even though chalcedony certainly has more history than opal.
But even the definition of fossils can leave us perplexed, in fact fossils are divided into 2 categories: true fossils, original remains more or less replaced by new minerals, and casts and traces, something that is not the animal itself. So an internal cast of a gastropod is not a true fossil because it is only the internal shape of the shell. It has nothing to do with the animal and cannot be classified. In this scheme, stromatolites would be fossil tracks even if they are bioconstructors of reefs. Furthermore, all carbonate rocks in the world should fall into this second category because all carbonate is extracted from the seas in the form of micrite, that is, bioprecipitated by bacteria. And this lack of clarity in the definition of fossil is a big problem when certain governments try to protect the paleontological heritage by prohibiting the collection of ammonites, but then give permits to cement factories for the extraction of carbonate rocks that often contain the same ammonites. It often comes to the point of destroying entire coral reefs that are crushed to make gravel.
In my recent book "Biominerals" (which you can find on my website) I analyzed thousands of minerals that have grown with the help of microbial colonies, mostly autotrophic archaea, that is, that draw their energy from chemical reactions in the environment, the same reactions that produce the precipitation of minerals. The variety of minerals involved is immense and the quantity of geometries developed makes the biological activity in the precipitation of these minerals unquestionable. At this point the distinction between minerals and fossils becomes superfluous, these are biominerals, which are both things and can fit perfectly in both mineral and fossil collections.
If we want to answer the initial question correctly, we must first rewrite the definitions.

[Herwig]

Dear Marco,
you wrote about so many things, it was hard to digest, so to speak.

Let's focus on two things. You state:
" I came across a bivalve in fluorite from Belgium that seems very unique to me, as it appears to be made of monocrystalline fluorite."
=> why do you think it is monocrystalline? There is no way for you to see that with the naked eye.

You also state:" pseudofossils and mineraloids, two absolutely useless and decidedly unclear categories."
=> why would pseudofossils be unclear and be absolutely useless?

[marco campos-venuti]

Dear Herwig,
I like to write about debatable things in my posts so I really appreciate your questions.
1) "why do you think it is monocrystalline? There is no way for you to see that with the naked eye."
I see a transparent fluorite, so it is not microcrystalline. Most fossil casts are microcrystalline, like emerald gastropods. This bivalve is on top of a fluorite crystal, so I assume this crystal grew on top of the empty fossil cast and filled it. Unusual, but not so strange.
2) "pseudofossils and mineraloids, two absolutely useless and decidedly unclear categories"
Science needs clear definitions and definitions must be made in positive sentences, not negative. It is absurd to say that a coral is a pseudo-tree, either we know it is a coral or we give it a provisional name until someone clarifies the doubt.
PSEUDOFOSSIL: "it looks like a fossil but is not." First of all, what kind of fossil does it look like? And if it's not a fossil, then what is it? The term was basically coined for manganese dendrites. According to my studies, dendrites are actually fossils, but that's not the point. If we analyze a dendrite it is made of at least 5-10 different minerals, so it would be a rock, not a mineral. A marble is made of only one mineral, but no one says it is a mineral, it's a rock. There are other examples of pseudofossils and most are either rocks or fossils of dubious origin. The cat marking its territory!
MINERALOID: "it looks like a mineral, but it is not." Again I wonder what mineral would it look like? Some examples: amber is actually an organic compound so why forcefully introduce it in a mineralogy text book? I don't know of any mineral that resembles amber. Obsidian is a rock, lignite is a fossil, fulgurite is a rock, limonite is a rock, pearl is a solid part of a living being made up of various compounds, etc. Most are rocks, fossils or organic compounds, again the cat marking its territory!
CRYPTOCRYSTALLINE: it is crystalline even if we cannot see the crystals. With all the technology we have! The term was coined for jasper and flints. I have shown that they are a polymer that has a type of crystallinity that is not the same as that defined in mineralogy. So from a mineralogical point of view a polymer is not crystalline, does not form euhedral crystals and does not belong to a crystal system. So either we accept some polymers as minerals, such as opal, chrysocolla and others, or we decide that all amorphous materials are not minerals. With the risk that opal becomes a field of study for chemists. Again the cat marking its territory!

[Roger Warin]

Marco, Herwig,
Herwig is a legalist. I prefer the laws of nature.
The opal is not a mineral species... “strictu sensu”. However, this was not the opinion of the IMA. Occult influences guided the IMA in a field dominated by a “lato sensu”, more consensual.
For the chemist, opal belongs to the field of inorganic chemistry since it is not an organic compound, the latter being composed mainly of carbon.
My point of view (but you don't discuss my opinions much) is that the shell of a mollusc is an amorphous biomineral, because without a crystal lattice, based on calcite and partially on aragonite.
That said, a certain structure may remain, derived from the biopolymer that gave birth to it. Then the biopolymer, having become useless, disappeared.

Nothing is simple in Earth sciences.
I still regret not having bought that fossil that Roger Titeux suggested I buy in 2002. An emerald shell !
What was I thinking that day? All I have left is the photo. I think that this fossil is currently in France...
In my opinion, the mollusk did not wait for an incompatible emerald to arrive before it was born. Calcite (and aragonite) were enough for the mollusk. It needed a carbonate.
How did it turn into beryl? These are the mysteries of Gachala (Colombia). The carbonates of the shell have been replaced by beryl, a substitution of carbonates by beryl.
It is an emerald pseudomorphosis

As for Marco's magnificent fluorite, I would gladly put it in my showcase!
I believe it is a pseudomorphosis, just like Titeux's emerald. I consider these pseudomorphoses to be minerals but not mineral species.

[Roger Warin]

It's better with the photo.