vitreous
lustre ; the colors are blue, red, green, and brown, of different
shades. Several colors may often be observed in one and the same
crystal, as, for instance, in the rubellite from Paris, in Maine, and
Chesterfield, Massachusetts, inclosed by the green tourmaline; and the
color often varies in its different layers.
Tourmaline
scratches glass slightly, but is scratched by topaz; its powder is
white ; its specific gravity is 3.0 to 3.3; it becomes electric by
rubbing, that end having the greatest number of faces being positive,
the other negative. When tourmaline is heated it exhibits polarity, the
most modified extremity becoming positive and the other negative. In
this particular it resemble3 other hemihedrically modified crystals. At
a certain temperature it loses its polarity, but exhibits it again on
cooling; its polarity continues with the decrease of temperature until
it reaches 32° Fahr.; a continued increase of cold re-excites the
electric polarity, though with reversed poles; if the excited crystal
be broken, each part thus produced will equally possess polarity, and
even in the powdered state it retains its pyro-electricity. Before the
blowpipe it intumesces more or less, does not fuse, but vitrifies on
the edges; turns green, then yellow, then red, then milk-white, then
blue, and then black. Borax dissolves it pretty easily into a clear
bead.
The
chemical composition of tourmalines varies greatly: they are composed
of alumine, silica, oxide of iron, oxide of manganese, and boracic
acid; those from different localities contain either potash, soda,
lithia, or calcia. The following are the different varieties, not
including, however, the white, yellow, and black tourmaline, or
schorl, they not being used as gems :
1. Siberian tourmaline (siberite, rubellite, apyrite), which is of a carmine or hyacinth red, purple or rose red, passing
