New Mexico Mineral Symposium — Abstracts

Rock Springs Canyon on the east side of the Organ Mountains contains some of the larger miarolitic cavities in North America. These deposits were first found and mined by a German named Hoffer in the early 1940s. The gentleman was an entrepreneur and found the deposits while on a hunting excursion. Hoffer mined the deposits for its exceptionally large, clear quartz crystals when the demand for radio quartz made it an economic opportunity. Because of lack of documentation and the obscurity of this locality, the location of the deposit was lost to the mineral-collecting community for over 40 years. It was Hoffer's friends who were responsible for my finding the deposits in the mid 1980s.

The miarolitic cavities occur in the Sugar Loaf Peak quartz monzonite porphyry phase of the Organ Mountain batholith. The largest and most diverse miarolitic, in terms of mineral species, has been named "The Pit." All the major quartz specimens were mined out during the original mining; consequently, the specimens retrieved in recent years were left in the dumps, and many are damaged or weathered. The mineralogy was not documented during the original mining; all of the following information is either verbal communication or information I collected first hand.

Albite—Crystals of extremely good quality are common. Single crystals larger than 1 cm and radiating groups of twinning crystals in parallel growth forming pinacoids to 5 cm have been found.

Apatite—Hydroapatite is found in small crystals in abundance whereas larger ones up to 5 x 3.5 x 4.5 cm are very rare. A few of the larger ones contain inclusions of small dodecahedral pyrite crystals. The apatites vary greatly in morphology and clarity. Faceting-grade material is quite rare although some gems have been cut. All of these, to my knowledge, are smaller than 10 carats.

Orthoclase—The most abundant mineral in the cavities, large baveno and some manebach twins are common. The largest known crystal is 18.2 x 8.3 x 8.6 cm and like most, has some magnetite growing on it. In general, the crystals have a secondary overgrowth of perthite, and some contain cores of chatoyant sanidine.

Quartz—I was told that the core of "The Pit" contained in excess of 40 crystals, 2 to 4 ft long. To my knowledge, none of these survived. The Smithsonian has in its possession a group of five smokey crystals with secondary twinning on three of the faces. The largest crystal is over 12 inches long.This specimen came from one of the smaller miarolitics. Some of the crystals have inclusions of pyrite, some are bent, some are floaters with no real morphology, and many are double terminated.

Titanite—Large root beer-colored sphenes up to 5 x 5.5 x 1.5 cm have been collected. The larger sphenes are twinned and very rare; smaller ones are much more common.

The deposit also has epidote, magnetite, biotite, molybdenite, pyrite, and perthite as part of its mineralogy. The finest specimens contained several of these above minerals on the same specimen.

In conclusion, I would say that the tailings have been extensively searched, and the prospect for more specimens is slim.