solution of caustic potash; in other respects its chemical characteristics are the same as quartz.
The
precious opal is found in claystone porphyry at Czernowitza; between
Kaschau and Eperies, in Hungary; occasionally near Frankfort; and at
the mines in the province of Gracias, Honduras, South America : the
"fire" opal at Zimapan and San Nicolas, in Mexico, the Faroe Islands,
etc.: the common opal in Hungary, Faroe Islands, Iceland, Giant's
Causeway, Ireland, Cornwall, and near Smyrna : cacholong occurs in
small masses on the river Cach, in Bucharia—whence its name—and also in
Iceland.
The
precious, or noble opal is one of the most beautiful gems in
existence; when held between the eye and the light it appears of a pale
milky-reddish blue, but when seen by reflected light it displays all
the colours of the rainbow, in flakes, flashes, or specks,—in fact, all
the colours of the most beautiful gems are here united in one. When the
colours are in small flakes, distributed over the surface, it is termed
by jewellers "harlequin" opal, on account of its resemblance to the
motley tints of the harlequin's dress. When fine, these are much
prized; but most persons prefer stones having the variously-coloured
fire in large flashes. This marvellous play of colour is thought to be
occasioned by nearly invisible fissures ; the Abbe Haiiy, however,
ascribes it to thin films of air filling cavities in the interior.
Opals are always cut en cabochon on both sides, and the true beauties of the gem only display themselves when the
