112 PRECIOUS STONES.
Pyrites is the more abundant form of this compound of iron and sulphur. It was largely used in jewellery in the eighteenth century, and
is often incorrectly spoken of as marcasite. It takes a fine polish and
presents the appearance of a metal. It is of no value whatever from a
commercial point of view, although a good deal of time and trouble were
frequently spent in cutting specimens of it into faceted forms, such as
single " roses." Pyrites was used by the ancient Mexicans along with
turquoise and obsidian for their mosiac inlays and incrustations. In
the Christy collection of the British Museum is a Mexican mask, in
which the eyes are represented by hemispheres of pyrites.
H.EMATITE.
Black
haematite is an oxide of iron occurring under several common names, as
specular iron ore, iron glance, and micacious iron ore. Its powder is
red, though a perfectly polished artificial or natural surface presents
a metallic black lustre with slight iridescence. It has been employed,
cut en cabochon. to simulate black pearls. The hardness of the
densest haematite is 6.5, and its specific gravity 5.3. It contains in
100 parts :
Amber
Is
hardly to be reckoned amongst precious materials of mineral origin, for
not only is it comparatively abundant, but it is an almost unchanged
vegetable product, a fossilised resin of certain conifers of tertiary
age. Its specific gravity is about 1.08, and its hardness, 2.5. When
traces of moisture and ash are deducted it contains in 100 parts about :
Amber,
whether from the Baltic shores, Sicily or the coasts of Norfolk and
Suffolk, is essentially the same substance, although the Sicilian amber
sometimes exhibits a deeper and redder or
