Part 19

Diopside is cut and sometimes sold in Turin and in Chamouny as a gem stone, but no great quantity of this mineral is used for ornamental purposes.

The hardness of diopside is 5 to 6; specific gravity, 2.9 to 3.5; lustre, vitreous to greasy. It is transparent to translucent, brittle, cannot be dissolved by acids, and melts before the blow-pipe. It is composed of:

Silica 54 Lime 24 Magnesia 18 Ferrous oxide 4

This mineral is grayish-white to pearl-gray, and greenish-white to greenish-gray. The best green transparent specimens are from the Mussa Alp and Zillerthal, but it is also found in the Urals and the United States.

FLUOR SPAR.

This mineral occurs in many colors, often approaching the finer gems in appearance, and bearing the commercial names of false ruby, false emerald, false topaz, etc., etc., according to its color.

Fluor spar is brittle, 4 in hardness, has the specific gravity of 3.1 to 3.2, single refraction, is transparent to translucent, has a vitreous lustre, phosphoresces when heated, is attacked by acids, and melts before the blow-pipe. It is composed of:

Fluorine 48.7 Calcium 51.3

White, yellow, green, rose- and crimson-red, violet-blue, sky-blue, and brown, wine-yellow, greenish-blue, and gray are the colors of this many-tinted mineral.

Fluor spar is found in England, Norway, Baden, Nova Scotia, Thuringia, the Alps, Saxony, and the United States.

Large pieces of this mineral are made into beautiful vases and ornaments.

HYPERSTHENE.

Handsome specimens of hypersthene or Labrador hornblende are used for ornamental purposes.

This mineral is found in crystalline masses, has the hardness of 6, specific gravity 3.3 to 3.4, lustre pearly to metallic. It is translucent to opaque, brittle, and fuses before the blow-pipe. It consists of:

Silica 54.2 Magnesia 24.1 Protoxide of iron 21.7

Hypersthene occurs in dark-brown, green, grayish-black, greenish-black, and jet-black colors, and is found in the isle of Skye, the Hartz Mountains, Saxony, Labrador, Greenland, Norway, Sweden, Bohemia, Thuringia, and the United States.

QUARTZ.

The quartz group is the largest and most diversified among precious stones. Quartz occurs massive, in concretions, and in confused crystalline masses.

On account of the abundance of the massive kinds, such as jasper, agates, onyx, etc., some writers place the quartz group under the head of semi-precious stones, and lately the United States customs authorities have gone further in that direction, and have ruled that “because of the abundance and comparative cheapness of agates, onyxes, etc., they were no longer precious stones.” This position, however, the custom-house speedily abandoned, and, for dutiable purposes at least, the quartz family, in all its ramifications, is recognized as belonging to the precious stones.

Harder than the tourmaline, turquois, or opal, as hard as the chrysolite, and nearly as hard as the garnet or emerald, there is no reason why the crystallized varieties, such as amethyst, cairngorm, false topaz, chrysoprase, and even the cat’s-eye and finer onyxes, should not be classed among the precious stones.

Some more plentiful and less beautiful varieties of quartz are not valuable, and they take the same position in the quartz family that the huge imperfect crystals do in the beryl group. Whenever the specimen is sufficiently beautiful to be cut and polished for setting in jewelry, it should be included under the precious stones.

Quartz crystallizes in the rhombohedral system, and many varieties are found massive and compact. The cleavage is indistinct but can sometimes be found by plunging a heated crystal into cold water. The hardness of quartz is 7; specific gravity 2.5 to 2.8, the purest kinds being 2.65; the lustre is vitreous to resinous, and fracture conchoidal.

Quartz is tough, brittle, and feels cold; it becomes positively electric by rubbing, shows phosphorescence in the dark, and gives sparks if struck with another piece of quartz or with steel.

Quartz is transparent to translucent, semi-translucent to opaque, doubly refractive, and does not melt before the ordinary blow-pipe, but may be melted with the oxyhydrogen blow-pipe. It also melts with soda to a clear glass, and is soluble in fluohydric acid.

Quartz is composed of pure silica

Oxygen 53 Silicon 47

Some of the impure varieties contain oxide of iron, carbonate of lime, clay, and other minerals.

CRYSTALLIZED QUARTZ.