|
CHAPTER XV.
|
||
|
|
||
|
OPAL.----PEARL.
The name opal, it is thought, was primarily derived from the
Sanskrit upala, meaning a stone or rock, more directly from the Greek and Latin hopallios, opalus. Of all precious stones, says Pliny, the opal is the most
difficult to describe, since it seems to combine in one gem the beauties of many other species, — the fire of the carbuncle, the purple of the amethyst, the green of the emerald, and the yellow of the topaz. Many speculations have been advanced by chemists in
regard to the causes of the remarkable peculiarities of this precious substance, some maintaining the opinion that its beautiful play of colors depends principally upon the quantity of water it contains, which varies greatly in different varieties, while others believe that water is not absolutely essential to produce this striking effect. The brilliancy of the tints is heightened by heat, unless too
intense or too prolonged, when the colors vanish entirely. This result seems to indicate that the presence or quantity of water has some connection with the development of the wonderful iridescence of the opal. It may be of some interest to know that so distinguished a
philosopher as Sir Isaac Newton believed the play of colors in this gem were the result of the refraction and reflection of light caused by the exceedingly small and numerous fissures crossing it in every direction. 280
|
||
|
|
||