390 A POPULAR TREATISE ON GEMS.
it
has a perfectly foliated structure; a glittering and metallic lustre;
is transparent and translucent; very fusible and elastic; its colors
are white, green, black, brown, peach-red, yellowish, and bluish ; it
has a specific gravity of 2.7. It is found in primitive rocks, and
forms an ingredient in granite, gneiss, mica slate, and other rocks,
where it more or less predominates; its localities are, therefore,
universal, but in Siberia it forms large beds, and is quarried for
special purposes, such as a substitute for glass windows; and although
the United States afford ample localities of it, yet a few years ago
quantities were imported here for the doors of Nott's stoves.
The plumose mica is
a beautiful variety, and derives its name from its resemblance to a
quill or plume, the lamellar or fine delicate crystals diverging in
such a manner as to present this appearance. It is of a pearl-gray
color. It is found in the United States, at Williamsbury, Mass.,
Hartford, Conn.,, and many other places. The green mica is of a beautiful grass-green color, and is found in Brunswick, Maine. The rose-red mica is
a very beautiful mineral, and is found in numerous places, in this
country; principally at Goshen, Chesterfield, Mass.; Acworth, N. H.;
Bellows Falls, Vt., &c. Mica may, when of good colors, be used for jewelry and other ornaments, as well as the lepidolite.
PYRITES.
This
mineral is called sulphuret of iron, iron pyrites, and markasite. It
occurs crystallized in many forms; such as the cube, octahedron, and
dodecahedron ; also massive, disseminated, capillary, and cellular; it
has a conchoidal fracture; a brilliant metallic lustre; its colors are
bronze, yellow, brass-yellow, and steel-gray. This mineral takes a very
high polish, and from, its fine lustre looks extremely
