FMF - Friends of Minerals Forum, discussion and message board

[Carles Millan]

[Don Lum]

[Carles Millan]

[Don Lum]

I don't know if there are any wiser people on the Forum than you, Carles. In any event I don't have anymore specimens like that to post.

Sincerely,

Don

[Mark Ost]

That is an interesting question as many fossils are permineralized with minerals replacing the original material that was biogenic. On the other hand the definition of a minerals is a non-organic substance with definite but not fixed orderly structure and chemistry. I suppose the definition hinges on if the specimen is of biological origin and was itself alive. That claim cannot be made of say feldspar or tourmaline. Of course some minerals are the result of biogenic action but they were never, by definition, alive.

I suspect this is a lot like the planet debate as there is no real concrete definition of planet outside of the Greek origin "Planitos"

This is a toughie.

[Cesar M. Salvan]

Carles, If I got the point that drives your question, there are some cases of minerals that are true fossils itself. An example is the Fichtelite (C19H34). From a chemical point of view, Fichtelite is a saturated cyclic hydrocarbon and is a fossil form of some bioterpenoids, mainly from conifer resins. The Fichtelite, apart of a mineral, is a "molecular fossil". Other examples are Simonellite and Hartite.

So to the question 'when can a fossil be also considered a mineral?' the response is when the existence of the mineral itself depends on the fossilization process. i.e. the mineral does not exist apart of a fossilization. As in the case of fichtelite.
We consider these minerals as molecular fossils because we can trace the chemical structure to the original, biological structure. But caution, not all organic minerals are molecular fossils.

[Pete Richards]

The basic definition of a mineral is that it is a naturally occurring inorganic chemical. The question of biogenic origin leads to all kinds of philosophical knots.

Sulfur crystals may precipitate when bacteria act on naturally occurring hydrogen sulfide or hydrocarbons; are these minerals? What about pyrite, which may result from bacterial action?

Brachiopods produce shells made of fibers of calcite, with minor if any organic matter between them. During diagenesis, the organic matter is replaced by calcite. Is the replacing calcite a mineral, but not the biologically-precipitated fibers?

Echinoderms produce porous plates of single crystal calcite; during diagenesis the pores fill epitactically with calcite to form complete single crystal plates, easily detected in limestones because of the calcite cleavage. Are these (even the infilling) not minerals because the template was formed by biological action, and the template dictated the orientation of the later infilling?

Many clams and other mollusks make their shells at least partly of aragonite, which often is replaced in the fossil by calcite, which is often blocky and preserves none of the subtle texture of the original shell. Is this calcite a mineral?

What about minerals that form in voids inside clam shells - anapaite and vivianite come to mind?

The ultimate perspective is recent work (sorry, I should be able to quote a source, but I can't) which points out that early biological evolution produced photosynthesizing primitive plants that led eventually to an oxygen-rich environment, which is a major factor in forming most of the known minerals - many oxides and hydroxides, sulfates, carbonates, phosphates, etc.

The question of whether silicified ammonites or brachiopods or pyritized trilobites or ammonites are minerals hangs on whether the precursors are minerals or not. If the precursors are minerals, then the replacements are minerals. If the precursors are excluded because of a biological influence, then the argument about the replacements starts all over again. What a pain!!!

My own perspective is that if an inorganic chemical substance originates as a consequence of biological activity, and it is known to occur in nature (e.g. calcite and aragonite, pyrite) without immediate biological mediation, it is a mineral. Unless it is known to have been formed by intentional or artificial intervention by humans (e.g. growing zincite or antimony or silver or suifur crystals, or abandoning tin cans and lead batteries in environments where they lead to micro-cassiterite or cerussite formation in the midst of a vast region of innocent sedimentary deposits) we must consider these things to be minerals. Slag heaps are certainly an important special case. Inorganic chemicals known only as direct biological precipitates are up for discussion.

My opinion and one Euro can perhaps buy you a good cup of coffee....

[Pete Richards]

[Mark Ost]

Ha! Oh yes; I have to be careful as there are so many exceptions and fuzzy areas. Tourmaline just popped into my head as most likely not having any connection to biogenesis. I once asked a professor how we could really say anything since it seemed we knew so little. His astute answer was they don't give degrees for saying nothing at all.

[Mark Ost]

Lead batteries lead to micro cassiterite?................oh man, I could show you the yellow brick cassiterite road then! 127,000 ppm of lead (soil) in a road underlain by old car batteries ground up. Maybe I should open a cassiterite mine!

[Pete Richards]

[gemlover]

Personal viewpoint: The fossil may be composed of mineral, but it is not itself a mineral, it is a cast, etc. of the animal. A fossil may also be composed of mud or other materials, that may not be a single mineral. I guess it is a discussion of semantics.

JOHN

[Carles Millan]

[Carles Millan]

[Mark Ost]

I would prefer transforming it to gold. Actually mining is not too far from how it was removed!