PRECIOUS STONES 111
of
various shades of red, running to violet-blue. In the Isle of Elba
colorless specimens, with short black terminations and the reverse,
occur.
The
crystal is hemihedral, the two extremities terminating differently,
and, in common with others showing that peculiarity, becomes electric
by heating, exhibiting positive electricity at one end and negative at
the other. Mr. Streeter mentions an interesting experiment by Professor
Miers: If a mixture of red lead and flowers of sulphur be sprinkled
through a sieve on a tourmaline which is slowly cooling after being
heated, the powder separates, the red lead, positively electrified by
friction through the sieve, is drawn to the negative end of the
tourmaline, and the sulphur, negatively electrified, seeks the
positive end.
