matrix
is much fancied for this purpose, as the mottling of brown in the blue
produces a very rich effect. The matrix of gems from some American
mines is flinty, and both the gem and the matrix are very hard which
affords possibilities of a high polish, but as the flint sometimes
penetrates the turquoise it is apt to break it.
Occidental
turquoise, formerly used extensively, is odontolite, made from fossil
bone, coloured by a phosphate of iron; it is still mined to a small
extent in the vicinity of Simor, Lower Languedoc, France. This western
" turquoise " loses its colour in artificial light, and, when heated,
gives off an offensive odour caused by the decomposition of animal
matter. Its weight is lighter than that of turquoise, and it does not
give a blue colour, with ammonia, when dissolved in hydrochloric acid,
like the genuine.
The
conditions peculiar to the demand for turquoise at present in America
are like those affecting opals; the very choicest specimens are highly
prized and readily sold, while the average specimens are considered
with indifference.
