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218 The Opal.
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has
the curious property of improving by the warmth of the hand, which
brings out the brilliant tints for which this stone is so famed.
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HUNGARIAN OPALS.
The Precious Opal, used in jewellery, was formerly obtained almost exclusively from Hungary. It was called Oriental Opal by
the Greek and Turkish merchants, who obtained it from the celebrated
mines near Czerwenitza, and then carried it to the East for the purpose
of giving the title Oriental to it, which always conveyed a sense of
goodness and value to stones.
The
Hungarian Opal was found in the Tokai-Esperieser mountains, not far
from Czerwenitza, the principal mines being in the Libanka mountain,
west of Dubnik. It is believed that it was from this district that the
ancient Romans obtained their Opal. The matrix of the gem is an old
lava of brown or grey colour, known as andésite. In the clefts and
cavities of this rock, especially in the decomposed part, the Opal is
irregularly distributed as veins and nests. It is probable that
alkaline thermal waters, from volcanic sources acted upon the rock,
decomÂposing some of its silicates and setting free the silica, which
was deposited from the solution in a gelatinous condition and
solidified in the form of Opal.
The
opal mountains have been extensively worked by subterranean galleries
of great extent ; the rock being brought down by blasting, and the
shattered fragments then carefully picked over by hand. Most of the
Hungarian Opal is of the common variety, and specimens displaying vivid
colours fit for jewellery are comparatively rare.
There is, in the Imperial Cabinet of Vienna, an Opal
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