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Darwin-L Message Log 1:174 (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.


<1:174>From mhallbey@magellan.geo.usherb.ca  Sun Sep 19 18:34:47 1993

Date: Sun, 19 Sep 1993 19:32:50 -0400
From: mhallbey@magellan.geo.usherb.ca (Mryka Hall-Beyer)
To: darwin-l@ukanaix.cc.ukans.edu
Subject: Classification in mineralogy

   The classification discussion has lured me out of
lurking! I was trained as a mineralogist, but have wandered
far afield into remote sensing. My interest in the historical
sciences, apart from multi-temporal satellite images, is
personal.

   I will throw in a few comments on classification in
mineralogy. Its relevance is the lack of involvment with any
idea of teleology, nor contamination with baggage about
"higher" and "lower" forms. Yet many of the issues are similar
to those raised.

   Minerals are grouped together in two ways. The true
classification system is a tree, and is based on the chemistry
of the mineral. There are sulfides, sulfates, oxides and
silicates. The silicates are subdivided according to the SI:O
ratio. Further subdivisions occur on the grounds of structure,
and the finest distinctions are then made by chemical for-
mulae, with "subspecies" being solution series between
interchangeable atoms (example: % Fe vs Mg in a certain
crystal site).

   An unknown or possibly new mineral would be placed in
this system strictly on the basis of observation: what is its
chemical formula and what is its structure? Since these two
factors determine macroscopic properties, we often tentatively
classify minerals on the basis of appearance in the field. But
we are often wrong, as impurities in the mineral can change,
for example, the colour. We have our splitters and lumpers,
depending on whether one considers impurities to be just that
or to indicate a separate mineral species.

   The second classification is by association of the
mineral, and is used to inquire about the mineral's history,
and ultimately about the history of larger geological units.
This seems similar to environmental variation. In mineralogy
I have not heard any discussion that a metamorphic garnet
should be classified differently from an igneous garnet. Many
chemical differences are typical of a certain environment,
some are even diagnostic, but the environment does not enter
into the classification of the mineral.

   Likewise, associations of minerals can go a long way to
telling us the environment at the time of mineral formation -
temperature, pressure, liquid and gas phases, etc. I wonder if
this is in any way related to the geographic variation debate?

   These are pretty random thoughts, hoping to stimulate
some ideas among those who know about biological classifica-
tion than I do. In sum,

1.history or geography do not influence the classification
system in mineralogy. The system is built entirely on features
observable in the isolated mineral. The study of history and
geography is informed by mineral classification, but not vice
versa.

2. The classification system is nested, tree-like, but it is
not necessary to see the tree as in any way heirarchical, but
only as the grouping together of increasing numbers of
similarities.

3. Simplicity and complexity are in no way interpreted as
"better" or "more developed" or even "commoner".

-Mryka  mhallbey@magellan.geo.usherb.ca

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