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Petrified woood - silica is inert
Dan,
Petrification, as Bill Brady noted, is a mineralogical change: but not
neccessarily by silica. In the strict sense, petrification is the infilling
of the spaces in wood, bone, shell etc., with a new mineral; and the
subsequent loss or alteration of the original matrix (the wood, bone, shell
etc.). In the case of wood, it is the tubes and cell spaces that become
in-filled.
I am a palaeontologist, and while some of the museum's fossils are silica,
most are not. Wood, for example can be silica, but can also be iron pyrites
or calcium carbonate. It depends largely on the depositional environment
the fossil began forming in.
So you might want to check what the fossil wood is: silica fossils are
glassy in section when polished. Calcareous ones fizz with a drop of acid
(like vinegar).
Silica itself is effectively inert, both in freshwater and marine
conditions. Secondary inclusions, like metals, might be more of a problem
if they are exposed at the surface of your fossil.
All the best,
Neale.
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From Neale Monks' Macintosh PowerBook, at...
Department of Palaeontology, Natural History Museum, London, SW7 5BD
Internet: N.Monks at nhm_ac.uk, Telephone: 0171-938-9007
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