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180
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GEMS.
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The pyroxenum hedenbergite, from the name of the chemist Hedenburg, is dark -green and almost black ; it only contains protoxide of iron, to which there is sometimes united a quantity of magnesia.
In
general, pyroxenum of every quality is but little used, although well
adapted for jewellery, in making ornaments for mourning.
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LXXX.
PISOLITE.
This stone, which is commonly called pisinella stone, differs
from the oolite, to which it is related, in the larger dimensions of
the aggregated particles, which, in it, are composed of concentric
leaves.
Like
the oolite, it is composed of small spheres united by a calcareous
cement, and it is found of different colours — reddish, brown,
yellowish, and white.
It
looks well when cut and polished. It is found in the alluvial deposits
of the warm waters rising at Carlsbad, in Bohemia, and at the baths of
San Filippo, in Tuscany. Its name is derived from τίσος, pease, λίθος, stone, on account of its most common colour.
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