Darwin-L Message Log 1:189 (September 1993)

Academic Discussion on the History and Theory of the Historical Sciences

This is one message from the Archives of Darwin-L (1993–1997), a professional discussion group on the history and theory of the historical sciences.

Note: Additional publications on evolution and the historical sciences by the Darwin-L list owner are available on SSRN.

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<1:189>From mhallbey@magellan.geo.usherb.ca  Tue Sep 21 18:58:38 1993

Date: Tue, 21 Sep 1993 19:58:12 -0400
From: mhallbey@magellan.geo.usherb.ca (Mryka Hall-Beyer)
To: darwin-l@ukanaix.cc.ukans.edu
Subject: Re: Classification in mineralogy

	If you had something that was half sulfide and half oxide it would be
two different minerals. If the sulfur were combined with the oxygen it would
be a sulfate, which is another mineral altogether, on another tree branch.

	I'm not sure if I'm answering the question you're asking: if not,
reply and I'll try again. Perhaps the problem is in the subdivision of
minerals using the main anions or aions groups (not sure if that's a technical
term, even if I had spelled it right!). The solution series, like the sub-
stitutions of Fe for Mg, or of Al for Si for that matter, are among the
cations of the formula. The cation content is not the basis for the main
tree branches, but rather comes in farther along the branching when separating
different minerals within the same anion group (sulfides, silicates, etc.).
For example, a Mg pyroxene and an Fe pyroxene are two differently named
minerals, end members of a solution series called pyroxenes. Pyroxenes are
in turn a member of the silicates. An Mg oxide and an Fe oxide are not
pyroxenes at all, since they are not silicates. You put silica in their
formula and they turn into silicates, maybe pyroxenes if the structure is
right.

	Interesting question.
-Mryka

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