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PRECIOUS STONES.
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work
it into objects of great beauty. A sceptre of white jade was sent as a
present from the Emperor of China to Prince Albert of England.
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.
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