Composition of Tourmalines

TOURMALINE:

The tourmaline holds but a secondary rank among those gems that are used for ornament, but, from a scientific point of view, it is well worth attention.

The modern tourmaline is the lyncurium of the ancients. It is also called schorl, especially in Germany, from the name of a village in Saxony, where it is very abundant.

Its composition is very complex; there are, however, certain elements which are characteristic of it, namely, boracic acid, silica, and alumina. In all tourmalines, also, there is an alkaline base, sometimes potash, sometimes soda, sometimes lithia, or a mixture of all. There is found in it also magnesia, lime, oxide of iron, and oxide of manganese.

The tourmaline is always crystallized, and its crystals appertain to the rhombohedral system. The crystals are in the form of longish prisms, sometimes with six faces, sometimes with nine, and in this case, in consequence of the obliteration or partial obliteration of faces, they terminate in such forms as shown in Fig. 82.

The tourmaline assumes a great many colours, and accordingly receives a great number of names. The Isle of Elba produces specimens from white to black; a species from Siberia is a beautiful red; from the Brazils both green and blue tourmalines are brought; and from Sweden a fine indigo-blue called indicolite. Berlin-blue tourmaline is called Brazilian sapphire; and there are green shades, which are called Ceylon or Brazilian emeralds.