consists
in passing an electric current "into an exhausted bottle, in the lower
part of which is placed a small cylinder of charcoal, and from the
upper part are suspended pla tina wires or platina foils; the sparks
thereby obtained from the combustion of the charcoal are of a
reddish-violet color; after the lapse of one month, during which the
combustion continues, a little black layer of charcoal is depos ited
upon the platina; under the microscope they appear like very small
octahedrons, quite analogous to the diamond ; some were free from
color, and very brilliant.
GEOLOGICAL CHARACTERS.
The
origin, locality, and geological characters of gems are various; it was
formerly supposed that the trap formation was their matrix; but it is
ascertained that we find them distributed in rocks of different ages
and kinds, either as accidental mixtures—such as garnet in gneiss and
micaceous schiste—or in drusy cavities, such as the emerald, which
occurs in druses of argillaceous slate and micaceous schiste; and many
precious stones are found in gangues. Many gems are found at a distance
from their original bed, on secondary or diluvial strata, or ft the
beds of rivers, mixed with their sand. Thus, zircon is found in Ceylon
in regular beds; and likewise we find in Ceylon, after much rain, the
topaz, zircon, and other gems. This hapmens more frequently in the beds
of the rivers, and then the gems appear often in the shape of pebbles,
showing that those hard stones, carried away from their original beds,
have been rolled and rounded by the streams and rivers, although they
retain sometimes their crystalline structure, on account of their
hardness.
The discovery of diamonds in Russia, far from the tropical region, has excited much interest among geologists.
