Part 16

This variety of felspar is called orthoclase, adularia, and orthose, besides the commercial names of fish-eye, Ceylon or water opal, and in the yellow and red tints sunstone. Moonstone occurs in crystals and crystalline fragments, also massive and granular; its hardness is 6. to 6.5, specific gravity 2.4 to 2.6, refraction double, is not attacked by acids, and is composed of:

Silica 64.5 Alumina 18.5 Potash 17. With traces of soda.

This beautiful stone is the clearest of all varieties of felspar. It is colorless, or only slightly tinted with blue, green, yellow, and flesh-red, and is transparent to translucent.

The lustre is vitreous, and a brilliant pearly streak of white light plays from side to side.

The yellowish- and reddish-tinted specimens are called sunstones, and are quite rare. These sunstones must not be confounded with the avanturine or felspar sunstone.

Moonstones are found principally in Ceylon and on the St. Gothard in Switzerland, but also occur in Bavaria, Greenland, Tyrol, Dauphine, Norway, and the United States.

During the past few years, large quantities of moonstone balls, cut like whole pearls, have been used for jewelry—the stones being much sought as well because of their beauty as on the ground of the popular superstition that they will bring good luck to the wearer.

Small pieces or balls are not very valuable, but large perfect specimens command a good price.

SUNSTONE.

(AVANTURINE FELSPAR.)

Sunstone or avanturine felspar is a variety of oligoclase; grayish-white to reddish-gray in color, usually the latter; containing minute crystals of hematite, göthite or mica, which are imbedded and scattered through the stone, and give forth golden-yellow, reddish, or prismatic reflections. The hardness is 6 to 7, specific gravity 2.56 to 2.72, and lustre pearly or waxy to vitreous.

Sunstones are found near Stockholm, in Finland, the Urals, Ceylon, the Alps, Iceland, the United States, and other places.

AMAZON STONE.

(GREEN FELSPAR.)

The Amazon stone is a green variety of felspar, which was first found on the banks of the Amazon River, but now comes from Siberia and the United States. This stone consists of potash, alumina, and silex—is green in color but rarely clean, being discolored in places and usually covered with small white spots.

The Amazon stone is harder than glass, but is scratched by rock crystal. Its specific gravity is 2.5 to 2.6; acids do not affect it, and it melts with difficulty before the blow-pipe.

LABRADORITE.

Labrador stone or labradorite is sometimes known as opaline felspar, and was first discovered on the island of St. Paul on the coast of Labrador.

Labradorite is translucent to opaque, gray-green or brown in color, and has beautiful chatoyant reflections of brilliant blue, sea-green, and sometimes red and yellow, changing from one color to another. Labradorite is 6 in hardness, has a specific gravity of 2.62 to 2.76; a vitreous to pearly lustre, is brittle, fuses with difficulty before the blow-pipe, and is decomposed by muriatic acid. It is composed of:

Silica 52.9 Alumina 30.3 Lime 12.3 Soda 4.5

Large masses of this stone are found on the coast of Labrador. It is also found in Finland, Russia, and the United States. Because of the dark chatoyant appearance the name of œil de bœuf or ox-eye is sometimes applied to labradorite. Handsome specimens, cut cabochon, form pretty ring stones, and many effective engraved cameos have been produced by using the bright portion for the relief work and the gray dead part for the base.

CYANITE.

This stone is the transparent variety of disthene, and is sometimes commercially known as sappare. Cyanite is colorless to bluish-white, sky-blue, berlin blue, yellowish- and reddish-white, gray, and green.

The hardness is 5 to 7, specific gravity 3.45 to 3.70, lustre vitreous and pearly; it is infusible before the blow-pipe, but fuses with borax; is not attacked by acids, and is composed of:

Silica 36.8 Alumina 63.2

Cyanite is found in Switzerland, the Tyrol, Styria, Carinthia, Bohemia, Norway, Finland, France, South America, Scotland, Ireland, Siberia, the East Indies, and the United States. Clean specimens are not plentiful, and fine blue pieces have frequently been sold for sapphires. The cyanite can be distinguished from the sapphire by its inferior hardness and lighter weight.

LAPIS LAZULI.

Lapis lazuli, the sapphire of the ancients, is a mineral, translucent to opaque, ranging in color from colorless to an azure-blue, violet-blue, green, and red.