Gems and Precious Stones of North America – George Frederick Kunz


CHAPTER III. Turquoise.

TURQUOISE is a hydrated phosphate of alumina sometimes containing small quantities of copper, iron, or manganese. Its hardness is 6, and specific gravity 2.75. The finest varieties, which generally do not lose their color easily, have been for centuries found in small veins in a clay slate in the vicinity of Nishapoor, Persia.

Large quantities are brought from Egypt, but this variety, although dark-blue when found, often changes in a short time to a verdigris green. This mineral is found at Los Cerrillos, N. M. ; Turquoise Mountain, Cochise County, Ariz.; Mineral Park, Mohave County, Ariz. ; near Columbus, Nev.; Holy Cross Mountain, Col.; and Taylor’s Ranch, Fresno County, Cal.

The first-named locality is part of a group of conical mountains situated about twenty-two miles southeast of Santa Fe, N. M., and north of the Placer or Gold Mountains, from which they are separated by the valley of the Galisteo River. The rocks of which they are composed are yellow and gray quartzite sandstones and porphyry dykes. Probably the sandstones are of the Carboniferous period, and they are so much uplifted and metamorphosed that the sedimentary character is partly obliterated. William P. Blake describes the locality as being an immense pit, with precipitous sides of angular rock, projecting in crags, sustaining in the fissures a growth of pines and shrubs.

On one side, the rocks 1 tower into a precipice,and so overhang as to form a cave, at another place the side is low, and formed by the broken rocks that were removed from the top of the cliff. The excavations, which appear to be about 200 feet in depth and 300 or more in width, were made in the solid rock, and thousands of tons of rock have been broken out.

The lower part of the working is funnel-shaped, and is formed by the sloping banks of the debris or fragments of the side walls. On the debris, at the bottom of the pit, and on the bank of the refuse rock, pine trees are now growing. There are several other pits in the vicinity more limited in extent, and some of them, apparently, more recently excavated. Prof. Benjamin Silliman, Jr., who visited this locality in 1880, states : ” The age of eruption of these volcanic rocks is probably tertiary.

The rocks which form Mount Chalchihuitl are at once distinguished from those of the surrounding and associated ranges of the Cerrillos by their white color and decomposed appearance, closely resembling tufa and kaolin, and giving evidence of extensive alteration, due probably to the escape through them, at this point, of heated vapors of water and perhaps of other vapors or gases, by the action of which the original crystalline structure of the mass has been completely decomposed or metamorphosed with the production of new chemical compounds.

Among these, the turquoise is the most conspicuous and important. In this yellowish-white and kaolin-like tufaceous rock the turquoise is found in thin veinlets and little balls or concretions called nuggets, covered with a crust of the nearly white tuff, which within consists  generally, as shown on a cross fracture, of the less valued varieties of this gem, but occasionally affords fine sky-blue stones of higher value for ornamental purposes.

Blue-green stains are seen in every direction among the decomposed rocks, but the turquoise in mass is extremely rare, and many tons of the rocks may be broken without finding a single stone that a jeweler or collector would value as a gem. The waste or debris excavated in the former workings covers an area which extends over twenty acres at least. On the slopes and sides of these great piles are large cedars and pines, the age of which, judging from their size and the slowness of growth in this very dry region, must be reckoned by centuries.'”

It is well known that in 1680 a large section of the mountains suddenly fell in from the undermining of the mass by the Indian miners, killing a number of them, and that this accident was the immediate cause of the uprising of the Pueblos, which resulted in the expulsion of the Spaniards. On both the east and west side of the mountain, shafts have been sunk, which were intended to be connected at their base by a subterranean tunnel.

The entrance to the main mining shafts on the west side is 194 feet below the spot where the Indians originally began their excavations. (See Illustration.) Recently several caves have been unearthed extending from the level of the long-abandoned mine.

Some of the most curious of these openings, named the Wonder Caves, are about 75 feet northwest of Shaft No. 1, on the east side of the mountain, and appear to have been hermetically sealed by the Indian peons on abandoning the mine; their discovery was purely accidental. The Wonder Caves are almost 25 feet from the surface and run 100 feet from the apex of the mountain, being about 30 by 25 feet in width and from 6 to 8 feet in height above the debris.

The group resembles in shape the five fingers with the hand. Here were found numerous veins of turquoise from 1/2 inch to 2 inches in thickness, and strips of gold-bearing quartz cover the walls of the central cave. The bottom is composed of loose rock, almost 20 feet deep, which is supposed to have been thrown there by the Indians when the mine was sealed. The roof is supported by pillars from 10 to 20 feet thick. It is presumed that further explorations would bring to light openings through these walls, showing that the entire mountain was honeycombed by the ancients, and the pillars left by them to support the roof.

This information was obtained in 1880 by the efforts of the mining company under J. B. Hyde, who supposed that the mine could be worked for gold and turquoise ; but the effort, after the expenditure of thousands of dollars, proved unsuccessful. The only work that is carried on at present at the Los Cerrillos Mines is done in a very desultory manner by either the local lapidaries, poor whites, or Indians. It