Mineral Guide > Precious Stones > Turquoise gem stone

Turquoise gem stone

Turquoise gem stoneThis mineral differs from nearly all others held in favor as gems in not being transparent and never occurring in the form of well-defined crystals.

The opal is perhaps the only other gem of which the same may be said. In composition Turquoise is a hydrous phosphate of aluminum, the percentages being: Of water, 20.6 per centum; of alumina, 46.8 per centum, and of phosphoric oxide, 32.6 per centum. Thus, in composition as well as opacity turquoise differs from most other gems, they being usually silicates or some form of silica.

Besides the above ingredients, turquoise always contains a small percentage of copper oxide and, usually, iron, calcium, and manganese oxides in small amount. It is the copper compound which undoubtedly gives turquoise its inimitable color, that color to which it owes its chief charm as a gem. The color varies from sky-blue through bluish-green and apple-green to greenishgray.

Of these colors, the pure sky-blue or robin's-egg blue is by far the most highly prized, and is, in fact, the only standard color for the gem. Green is, however, the most common and the most lasting color of the mineral, and it is one of the faults of the gem that the blue shades often fade to green after being exposed to the light for a time.

In a stone of first quality, however, especially a Persian turquoise, such fading of color is exceptional.

A good turquoise also maintains its color in artificial light. The hardness of turquoise is 6, in the scale of which quartz is 7. It is, therefore, somewhat more easily scratched than other gems. Its specific gravity varies from 2.6 to 2.8, being about that of quartz. It does not fuse before the blowpipe, but turns brown and assumes a glossy appearance.

By the copper of the turquoise the blowpipe flame is usually colored green. When heated in a closed glass tube the mineral turns brown or black and gives off water.

Turquoise Artificially Polished picture
Turquoise Indian Amulet picture
Turquoise Natural picture
Turquoise Waterworn picture