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278 PRECIOUS STONES.
and
the brown Tourmaline occurs with them. In Bengal, and in the Sapphire
deposits of Kashmir, Indicolite is found, and Eubellite occurs near
Mainglon in Burma.
In
the island of Elba, near San Piero, both the colourless Acroite and the
red Rubellite are found in granite, and Rubellite is found at Penig in
Saxony, with green and blue varieties. Dravite is named after its
locality at the Unter-drauburg in the Drave district of Carinthia. It
is also found at Crawford in New York State, while in the same State,
in St. Lawrence County, fine Achroite occurs near De Kalb. In Maine at
Paris the green variety as well as Rubellite and Indicolite occur; in
Massachusets, Chesterfield and Goshen yield good Indicolite and green
Tourmaline, and also a rose-red but opaque variety; in California, at
Mesa Grande, both the red and green varieties occur.
The
technical use of Tourmaline in the construction of plates for the
polariscope should be mentioned; the slices are cut from the crystal
parallel to the vertical axis.
In
cutting Tourmaline as a gem due regard must be given to the colour
effect from the pleocroism. Deep coloured stones are cut so as to have
the table parallel to the vertical axis; but in the case of pale stones
the table may be normal to this axis, for in this direction the mineral
shows its darkest colour. Tourmaline is often parti-coloured, one end
of a crystal may be green, and this may gradually merge into pink at
the other end, being accompanied probÂably by a corresponding gradual
change from a Tourmaline of one composition to one of another. The
Rubellite from Paris in Maine often shows an outer green layer; a
certain amount of Eubellite has crystallised first, and then the
isomorphous green Tourmaline has been deposited in optical
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