; when broken, the interior has a pearly reflection, slightly
translucent at the sharp edges. Harder than the opal, this substance
takes a good polish ; it is unaltered under the action of the
blow-pipe, and its specific weight is 2'2.
cacholong is found in separate bits in the rivers of Bokhara, in the
Feròe Islands, in Iceland, in trapp rocks, and in Greenland. It is also
procured in France ; and in Champigny, near Paris, it is brought from
the caves of calcareous breccia, and some of it is hard, of bright
cleavage, whilst others are light, rough to the touch of the tongue,
and soft as chalk, and therefore of inferior quality, and to be
regarded as imperfectly formed.
is a variety of this stone called striped, coming from Feròe and
Ireland, which being composed of thin strata of white and opaque opals
over strata of cal-cedony, often bluish or greenish, makes very fine
cameos. Italian artists call it French stone.
stone is thus named from the province of Calcedony, in Asia Minor,
whence, in ancient times, it was procured in great quantities. It is a
variety of agate quartz, generally of a milky-white colour, sometimes
bluish ; and this last tint somewhat increases its value.