The
tourmaline is also found in a massive state, sometimes fibrous or
radiating. Under the blowpipe it swells up, and fuses into a sort of
slag. The crystals are occasionally found parti-coloured—for instance,
red internally and green externally, others blue and green, and
frequently in those found in Elba, red at one end, yellow in the
middle, and black or brown at the other extremity. When heated or
rubbed, the tourmaline acquires a different degree of electricity at
each extremity. If broken whilst in that state, the fragments, like
artificial magnets, present opposite poles.
The
tourmaline is cut upon a leaden or zinc wheel with emery, and polished
with tripoli. The transparent varieties are generally trap cut; the
opaque are faceted both above and below the girdle.
The
lapidary is obliged to bear in mind that this stone is only transparent
in one direction, and that, unless the table be parallel with the axis
of the crystal, an otherwise transparent stone will appear opaque on
looking through it. This stone was first brought to Europe by the Dutch
from Ceylon, and they gave it the name of aschentrekker, from its
sometimes attracting and sometimes repelling hot ashes when laid near
it for any length of time. The tourmaline was considered a chrysolite
when yellow, a sapphire when blue, etc.; and even now it is of no
uncommon occurrence to find it sold under other names, although the
quality it possesses of acquiring magnetic properties by means of heat
affords a ready means of distinguishing it from any other
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