336 GEORGE F. KUNZ 



has been rediscovered and described during 1902. Opal of 

 many varieties and colors is abundant here, in a porphyritic 

 dike, traced for a mile and a half, parallel to the creek, and 

 at times as much as 150 feet wide. Much of it is very beau- 

 tiful, but it is also very brittle, and goes to pieces in extract- 

 ing it, so that stones of any size are difficult to procure. 



There are many minor occurrences that have been noted 

 and many varieties of semiopal that may hereafter yield ma- 

 terial of some value in the arts. Gem opals, however, are 

 not yet produced to any extent, or with any regularity in the 

 United States, although there is considerable promise at sev- 

 eral points. 



Turquoise is a hydrated phosphate of alumina, contain- 

 ing small quantities of copper, iron or manganese. The min- 

 eral varies in color from a fine sky blue to many shades of 

 bluish green, and to apple green and dark green, which show 

 no blue whatever. The hardness of the mineral is 6, and its 

 specific gravity is 2.75. 



Turquoise was almost unknown in the United States 

 until 1890. A few specimens in collections of minerals attest- 

 ed its existence at some points in Arizona and Nevada, and 

 objects worked by the Indians of the southwest were known 

 to be abundant, but there was no production of it, and all the 

 turquoise used in jewelry came, as it had for centuries past, 

 from the mines in Khorassan, in eastern Persia. Since then 

 a remarkable change has taken place, and the southwestern 

 states and territories are now furnishing the main supply for 

 the world. Turquoise has been discovered at a number of 

 pointsandinlarge quantities and of fine quaUty . It is known to 

 exist in Arizona, New Mexico, Nevada, and southern Cali- 

 fornia, while some localities are reported in Texas and south- 

 ern Colorado. The main production is in New Mexico, in 

 Santa Fe and Grant counties, and at Turquoise mountain in 

 Arizona. The California localities operated b}^ the Hima- 

 laya and the Toltec companies are northeast of Manvel, in San 

 Bernardino county. At almost every point where the min- 

 eral is found there are interesting and conspicuous evidences 

 of ancient workings in pre-Columbian times; in many cases 

 these were plainly both extensive and long continued; stone 



