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OLIVINE.
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LXIX.
OLIVINE.
Silicate of magnesia, which receives the name from its colour.
It
is like the chrysolite, but less transparent and less hard. It is
coloured with iron. It is found in masses and also in round pebbles, as
frequently in France as in Italy, Scotland, Bohemia, Ireland, on
Vesuvius, and in many other places.
The cleavage of the olivine is imperfectly double, and its breakage is unequal and granulous.
Its specific gravity is equal to 3ยท240. Analysed it yields
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Subjected
to the action of the blow-pipe, with the addition of borax, it forms an
opaque button of dark glass: When put into concentrated acetic acid it
loses colour; this phenomenon indicates a great porosity, most rare in
the texture of gems of this kind, and a principal sign by which to
distinguish it from those which resemble it.
Olivine is found in pieces large and small, in basalts, in porphyry, and in lava : it is almost always with pyroxenic augite.
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