About the Properties, Historical Value, and Popularity of Turquoise

Turquoise is a popular gem mineral today, as it was anciently with the Persians and the Aztecs, whose name for it was chalchihuitl. Turquoise is a French word, meaning a Turkish stone, also the feminine of Turkish. Turquoise is an amorphous stone occurring in kidney-shaped nodules and incrustations; its colour is various shades of azure or robin's egg blue. Of Persian origin, it is supposed to be the stone anciently referred to, in Pliny's natural history, as callais, callaina, and callaica. In his catalogue of gems in the United States National Museum, Wirt Tassin applies to turquoise the names callainite and turkis; Cattelle says it is known to scientists as "callaite"; Oliver Cummings Farrington in his Gems and Gem Minerals describes callainite as a distinct mineral.

The hardness of turquoise is 6; specific gravity, 2.6 to 2.8; there is no cleavage; it is brittle and breaks unevenly. The lustre of turquoise is waxy and the colour is sky-blue, bluish-green, apple-green, and greenish-gray. The colour is liable to change, however, the blue becoming a pale green. Artificial means are resorted to for "improving" stones of a poor colour, but a washing in strong ammonia water will expose the fraud. This solution will not affect the colour of the true turquoise, but as soap and water does, possessors of rings set with turquoise should never wash their hands without removing their rings.

The chemical composition of the turquoise is a hydrous phosphate of aluminium and copper, and the principal components in a hundred parts are: phosphoric acid, 30.9; alumina, 44.50; oxide of copper, 3.75; water 19.

The exposure of turquoise to a sufficiently high degree of heat will extract the water and cause it to crackle.

The turquoise most highly prized comes from Persia, and the most celebrated are those from an old mine, the Abdurrezzagi in a district of the Nishapur province in the north-eastern part of the country. Less valued specimens come from Asia Minor, Turkestan, and the Kirghiz Steppes. The Egyptians mined turquoise in the Wady Maghara, in the desert of Sinai. Specimens from Arabia in modern times proved of little value, fading quickly when exposed to the light. The mineral has also been found in Victoria and New South Wales. The United States is constantly growing in importance as a source for supply for the world market for turquoise. A trachytic rock in the Los Cerillos Mountains near Santa Fe, aboriginally worked by the natives, is a well-known mine, and some beautiful specimens have recently been found there. Other localities are Turquoise Mountain, Cochise County, and Mineral Park, Mojave County, Arizona; Columbus, Nevada; Holy Cross Mountain, Colorado; and Fresno and San Bernardino counties, California. Record specimens come from the mines of the Azure Mining Company, Burro Mountains, New Mexico.

Because of the opacity of turquoise, it is seldom cut with facets, but in a round or oval form, with convex surface; as the pieces suitable for cutting seldom reach a large size big turquoise gems are almost unknown. Turquoise matrix is also used now for medium class jewelry, the cutting including both the stone and its matrix. The turquoise in a dark-brown 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.