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AXINITE
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This
is a mineral occasionally cut for gem purposes, but not extensively in
vogue. It furnishes a stone of a clove-brown color, transparent, and
with glossy luster. It is somewhat deficient in hardness, being softer
than quartz, though harder than feldspar. Hardness 6.5-7. Before the
blowpipe axinite fuses readily, giving a pale green flame. It is not
attacked by acids. In composition it is a boro-silicate of aluminum and
calcium, with varying amounts of iron and manganese. Besides occurring
of brown color, it may also be of blue, gray, or yellow shades,
although brown is the most common. Like epidote, iolite, tourmaline,
etc., axinite is strongly pleochroic, showing olive-green,
cinnamon-brown, and violet-blue in different directions, especially if
examined with the dichroscope. It crystallizes in the triclinic system,
usually in thin, broad blades, which so much resemble an ax that they
have given the name of axinite to the mineral.
The
best known occurrence of axinite, and that which yields the finest
crystals, is near Bourg d'Oisans, Dauphine, France. It occurs here with
albite, prehnite, and quartz. / There are several other occurrences of
the mineral in Europe and the United States, but few yield material of
sufficient size and transparency for cutting.
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139
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