TURQUOIS. 



This 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 

 Turquois 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 Turquois differs from 

 most other gems, they being usually 

 silicates or some form of silica. Be- 

 sides the above ingredients Turquois al- 

 ways contains a small percentage of cop- 

 per oxide and usually iron, calcium and 

 manganese oxides in small amount. It is 

 the copper compound which undoubtedly 

 gives Turquois 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 

 greenish-gray. 



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 

 Turquois, such fading of color is excep- 

 tional. A good Turquois also maintains 

 its color in artificial light. The hardness 

 of Turquois 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 Turquois the blow- 

 pipe flame is usually colored green. When 

 heated in a closed glass tube the mineral 



turns brown or black and gives off water. 

 Almost any of these tests will serve to 

 distinguish true Turquois from stones 

 used to imitate it. It has a conchoidal 

 fracture and waxy lustre. On account 

 of its opacity it is almost never cut with 

 facets like most other gems, but in a 

 round or oval form with convex surface. 

 The pieces desirable for cutting rarely 

 reach a large size so that big gems of , 

 Turquois are comparatively unknown. 



Much of the so-called Turquois used 

 in former times was bone-turquois, or 

 odontolite, made from fossil bone colored , 

 by a phosphate of iron. It is obtained 

 mostly from the vicinity of the town of 

 Simor, Lower Languedoc, France. It is 

 sometimes known as Western or Occi- 

 dental turquois, in distinction from the 

 Oriental turquois, most of which came 

 originally from Persia. It does not re- 

 tain its color by artificial light as does 

 true Turquois and may be further dis- 

 tinguished by giving off an offensive 

 odor when heated, owing to decomposi- 

 tion of animal matter. Further, it is 

 lighter than true Turquois and does not 

 give a blue color with ammonia when 

 dissolved in hydrochloric acid, as does 

 true turquois. 



The finest Turquoises have long come 

 from Persia, from a locality not far from 

 Nishapur, in the province of Khorassan, 

 Here the mineral occurs in narrow seams 

 in the brecciated portions of a porphyritic 

 trachyte and the surrounding clay slate. 

 There are several hundred mines in the 

 region and the entire population of the 

 town of Maaden derives its livelihood 

 from mining and cutting the stones. It 

 is said that $40,000 worth of stones are 

 taken from these mines annually. A 

 pound of stones of the first quality sells 

 at the mines for about $400 and is worth 

 more than double that price in Europe. 

 There are other Turquois mines in Per- 

 sia, but their product is comparatively 



170 



