Part 17

The principal color, however, is a rich, azure blue, sometimes shading into green, and having a vitreous to greasy lustre.

Its hardness is 5 to 5.5, specific gravity 2.38 to 2.42; it is decomposed by muriatic acid, and fuses before the blow-pipe to a white glass. It is rarely found clean, but has usually a number of veins and spots of a metallic nature. It is composed of:

Silica 45. Alumina 31.76 Soda 9.09 Lime 3.52 Sulphuric acid 5.89 and traces of iron, soda, and potash.

This mineral is found in Siberia, Transylvania, Persia, China, Thibet, Tartary, South America, India, and Brazil.

Lapis lazuli is sometimes employed for jewelry, and was for some centuries ground up and used to make the mineral paint known as genuine ultramarine. This paint is now produced chemically, and the more costly mineral compound is rarely used.

The imitation of lapis lazuli for jewelry purposes is also very easy, as metal filings can be readily introduced into the azure blue glass, and thus an imitation of the genuine stone produced, which is perfect excepting in hardness.

HIDDENITE.

The hiddenite is a variety of spodumene that has only been found in one locality, namely, Alexander County, North Carolina. This mineral was discovered by W. E. Hidden, and has been named after him.

The hiddenite is perfectly transparent, and varies from a pale yellowish- to a deep emerald-green, being very brilliant, and approaching the emerald in color. As this stone is rarely found large enough for cutting into gems, it is highly prized, and good specimens command a large price.

The hardness of the hiddenite is 6.5 to 7, and specific gravity 3.13 to 3.19; before the blow-pipe it melts to a clear glass, and it is attacked by salts of phosphorus. It is composed of:

Silica 64.35 Alumina 26.58 Lithia 7.05 with traces of iron and soda.

SPODUMENE.

Spodumene is sometimes cut and polished as a gem, but its peculiar cleavage makes it a bad stone for the lapidary to cut and the jeweler to mount.

Its hardness is 6.5 to 7, specific gravity 3.13 to 3.19, and lustre, vitreous to pearly.

Grayish-green, greenish-white, and sometimes yellow or faint red are the colors. Its composition is:

Silica 64.2 Alumina 29.4 Lithia 6.4

Acids do not attack spodumene, and under the blow-pipe it fuses to a white glass.

This mineral is found in Sweden, the Tyrol, Ireland, Scotland, and the United States.

DICHROITE.

Dichroite is sometimes known under the mineralogical names of cordierite and iolite, and commercially as saphir d’eau, or water sapphire. This stone is remarkable for pleichroism, sometimes showing three different colors in as many directions, and when properly cut has often the star formation of the corundum star-stones.

Water sapphire, as the blue specimens are called, is 7 to 7.5 in hardness, specific gravity 2.56 to 2.67, transparent to translucent, and frequently full of flaws. It is partially decomposed by acids, melts with difficulty before the blow-pipe, is vitreous to greasy in lustre, and is composed of:

Silica 49. Alumina 32. Ferrous oxide 7. Magnesia 9.

Besides the saphir d’eau, which is blue, dichroite occurs colorless, bluish-white, yellowish-white, yellowish-gray to yellowish-brown, indigo to blackish-blue, and violet. This mineral is found in Ceylon, Spain, Norway, Sweden, Tuscany, Greenland, and Bavaria. Sapphire is harder and much heavier than dichroite.

IDOCRASE.

Idocrase or vesuvianite was first found amongst the ancient ejections of Vesuvius, and it is still found at Vesuvius in hair-brown to olive-green colors.

Vesuvianite is 6.5 in hardness, 3.35 to 3.45 in specific gravity, transparent to opaque, lustre vitreous to greasy. It possesses strong double refraction, is attacked by acids, and melts readily under the blow-pipe. Vesuvianite consists of:

Silica 37.75 Alumina 17.23 Sesquioxide of iron 4.43 Magnesia 3.79 Lime 37.35

In colors, this mineral shades from brown to black, yellow, pale-blue, and green, and it is found at Vesuvius, Alps, Piedmont, Mt. Somma, Etna, Norway, Sweden, Spain, Hungary, Urals, and the United States.