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. | |