|
152
|
PRECIOUS STONES
|
||
|
|
|||
|
QUARTZ
Is a mineral which takes on more forms and colors than any other.
The
crystallization is rhombohedral, and it occurs usually in six-sided
prisms, more or less modified, terminated with six-sided pyramids; also
granular and compact.
Hardness, 7; specific gravity, 2.6 to 2.7.
Lustre waxy to vitreous ; transparent to opaque.
Seldom has even a trace of cleavage.
It
consists of pure silica. Some other mineral is often disseminated
through the opaque varieties: oxide of iron, chlorite, clay, etc.
The varieties result from different modes of crystallization or impurities, and are divided into three groups:
I. The vitreous, having a glassy fracture.
II. The chalcedonic, of subvitreous or a waxy lustre, and generally translucent.
III. The jaspery, opaque and with very slight lustre. Quartz is infusible before the blow-pipe alone, but melts
readily with soda, and effervesces. It is not attacked in any way by the three acids.
The
vitreous are known as amethyst, aventurine quartz, cairngorm, citrine,
prase, rock crystal, rose quartz, siderite, and sagenite.
The chalcedonic are chalcedony, chrysoprase, cat's-eye, carnelian, plasma, sard, onyx, and agate.
The jaspery comprise basanite, bloodstone, jasper, and others.
|
|||
|
|
|||