A Treatise on Diamonds, and Precious Stones/Chapter 2/Section 9
SECT IX.
On the Turquois.
The color of the Turquois is beautiful celestial blue, which migrates into pale blue, and is sometimes tinged with green. It is destitute of that lustre which distinguishes most of the precious stones; it is also opaque, and does not admit of a very high polish; there is, therefore, nothing but its very agreeable hue which can recommend it to the notice of the jeweller. The latter character it possesses in no inconsiderable degree, and retains it unimpaired by candle-light. It has always been fashionable; and although great quantities have been imported, so as to render small stones extremely cheap, yet it has continued to be in considerable demand.
The finest variety is called Turquois Vieille Roche, its texture is uniform and compact. This gem is highly valued in Persia and other Mahometan states, and on that account the most beautiful stones are seldom sent to Europe.
It is doubtful whether the substance termed Turquois Nouvelle Roche is a real Turquois: it is generally supposed to be a fossil bone, colored by Phosphate of Iron; it frequently exhibits evident marks of organization[1].
The turquois is much worn in necklaces, and in every part of ornamental jewellery, from the size of a pin's head, to that of an almond: it contrasts beautifully with brilliants, or pearls set in fine gold, and appears to most advantage when cut spheroidal.
The imitations of this gem are feebly translucent, and lose their beautiful tone of color by candle-light. They are also much inferior in hardness, and have a greater specific gravity.
- ↑ This supposition is strengthened by its chemical characters, the Nouvelle Roche always effervescing in acid, which has no effect on the turquois.