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.
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.