This
is a mineral possessing several interesting characters, and having
many qualities desired in gems, yet its use in jewelry is very limited.
It is comparatively common as one of the constituent minerals of
metamorphic rocks, but in its ordinary occurrences it is not suitable
for gem purposes. It is only when occurring in large, transparent
crystals that pieces suitable for cutting can be obtained. Its peculiar
green color is one of its most striking characters, enabling it nearly
always to be recognized. This color is a yellowish green, known as
pistachio - green, and is hardly possessed by another mineral. It
frequently, however, shades to black on the one hand and brown on the
other, so that it cannot be taken alone as a criterion for
determination. Epidote is quite strongly pleochroic; that is, it
exhibits different colors in different directions, being often green
in one direction, brown in another, and yellow in another. It is
usually cut so as to show the green color, and the stone must generally
be made quite thin to get the proper transparency. Epidote is a rather
hard and heavy mineral, its hardness being nearly equal to that of
quartz, and its specific gravity 3.2 to 3.5. It is brittle, and has a
basal cleavage. Its luster is vitreous to resinous.
In
composition it is a hydrous silicate of calcium, aluminum, and iron,
the darkness of its color increasing with a larger proportion of iron.
It is fusible before the blowpipe, but unattacked by acids before
fusing. The finest crystals of epidote for cutting come from the
Knappenwand, in the valley of the Pinzgau, Austrian Tyrol. Specimens of
these are shown in the accompanying colored plate. This occurrence was
discovered in 1866. Quite recently an occurrence of epidote, more
beautifully crystallized even than that of the Knappenwand, was
discovered on Prince of Wales Island, Alaska; but unfortunately these
specimens are too opaque for cutting. Being a rather heavy mineral,
epidote lingers among the pebbles of stream beds, and material suitable
for cutting is hence sometimes found in this way. Brazil and North
Carolina are localities where epidote of this sort has been found.
