New Mexico Mineral Symposium — Abstracts

A gem is defined as "a precious or semiprecious stone that may be used as a jewel or ornament when cut and polished." A gemstone is defined as "a mineral or petrified material that when cut and polished can be used in jewelry." Although probably best known for its turquoise deposits, New Mexico has a number of minerals and rocks that fit this definition. Two general types of true gem material occur in the state: single mineral grains that can be faceted or polished and mineral aggregates that can be cut, polished, and worn as ornaments. Additionally, some mineral specimens have historically been used as ornaments with little modification from their natural state.

Crystals of feldspar, olivine, fluorite, and quartz from New Mexico have been faceted into gems. Pale-- to golden-yellow feldspar from Pueblo Park in Catron County and near Hatch in Dona Ana County, described as bytownite but more likely labradorite, has been faceted into some very attractive gems. Peridot, the gem variety of olivine, occurs at Kilbourne Hole, a volcanic maar in Dofia Ana County and in the Navajo Nation associated with ultramafic intrusions. Fluorite is a common mineral in New Mexico that commonly occurs as large, transparent to translucent crystals. Although too soft to be used in jewelry, fluorite has been faceted into large stones for display. Grant County is known for the production of the moonstone variety of sanidine from a pegmatite in Rabb Canyon. This locality has produced both facet-grade material and samples that can be polished into small chatoyant cabs. Facet-grade amethyst is found in lithophysal cavities in rhyolite southwest of Mule Creek in Grant County (west of Brushy Mountain) and in recently rediscovered vein deposits in the Ladron Mountains in Socorro County. Non facet-grade material is also found in a number of ore deposits around the state. Beryl deposits in the pegmatite deposits of Rio Arriba, Taos, and San Miguel Counties have produced a disappointingly small number of goshenite, morganite, and aquamarine gemstones. Yellow apatite of sufficient size and clarity for faceting has been produced from the Organ Mountains. Green titanite crystals from northern New Mexico have also been faceted into small stones.

Mineral aggregates are here defined as masses of relatively fine grained minerals but typically are masses of a single mineral with minor impurities. Smithsonite from the mines of the Kelly district in Socorro County is an example. Crystalline masses of opaque to translucent blue or yellow smithsonite can be polished into cabochons or cut and polished, for example, into an emerald-cut stone. Luna County has produced some interesting polishing materials including dumortierite Al₇(BO₃)(SiO₄)₃O₃ and spurrite Ca₅(SiO₄)₂(CO₃) from zinc skarns in the Tres Hermanas district and agate from several localities. Turquoise has been produced from the Tyrone, Santa Rita, Hachita, and Hanover—Fierro districts of Grant County since pre-Columbian times in addition to the famous Cerrillos deposits of Santa Fe County. Ricolite, a commercial name for a mixture of serpentine and talc from Ash Canyon in Grant County, has been cut, polished, and carved into many interesting and beautiful shapes.

Some minerals have served as ornaments without any enhancement from their original form, other than cleaning. Native copper has been found in several districts, most notably Santa Rita, and served as ornaments for the earliest discoverers of the deposit. More commonly, the native copper was pounded around small rocks and fashioned into bells by, for example, the Mogollon culture ca 900 A.D. Azurite crystals and crystal aggregates (rosettes) have been collected from a clay-filled shear zone along the Barringer fault at Hanover Mountain in the Hanover—Fierro district. Small crystals have been matched and set in silver earrings.

Collecting in some of the named areas is restricted, whereas other areas are open. Information can be obtained from the New Mexico Bureau of Geology and Mineral Resources (http://geoinfo.nmt.edu) or from local mineral clubs.