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GEMS.
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LXXIX.
PYROXENUM.
This name
is given to certain substances found by Hauy, scattered in lava and in
rocks of igneous origin, to which he thought them quite foreign, whence
the name of ττνρ, fire, and ksanos, stranger.
For
a long time they were confounded with the amphibole, with which they
have in common the form of the crystal and its components, but in
diiferent proportions.
That
which distinguishes the pyroxenura from the amphibole completely is its
inferior brightness, its vitreous light, and, above all, its cleavage
in three different planes parallel to the base.
The
colours of the pyroxenum are black, dark green, white, and grey. Its
most common crystals are different prisms with oblique axes ; they are,
however, sometimes met with in irregular octahedral prisms, more or
less modified, and in pebbles either granular or of a dense substance.
All these crystals are generally small ; their specific gravity is from 3-l to 3·4, and their very variable conformation yields on analysis
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