New Mexico Mineral Symposium — Abstracts

Gemstone and specimen-grade amethyst occur along faults in Unaweep Canyon located approximately 20 mi southwest of Grand Junction, Colorado. A series of faults, ranging from N5OW to N8OW and mineralized with minor amounts of copper and silver, also carry fluorite, amethyst, and calcite. The Amethyst Queen mine is located along a vertical brecciated fault zone in a Precambrian biotite-muscovite granitic rock. The amethyst vein has been traced on the surface for more than 100 ft at an average width of 1.5 ft and is known to extend 22 ft downward. Amethyst crystals, which occur as broken plates and loose crystals in a calcite cement, rarely exceed 1 inch in diameter and exhibit pronounced color zonation as reflected by Brazil Law twinning. Only about 1 percent of the crystals are gemmy; however, Siberian-grade faceted stones of several carats have been produced. Gemstone mining has continued intermittently for the past 8 years.

In the fall of 1985 a new occurrence of amethyst on fluorite was found approximately 0.75 mi from the Amethyst Queen mine along the same fault system. Amethyst crystals, averaging 0.25 inch across and coating apple-green fluorite octahedra, occur in mineralized Wingate Sandstone. Fluorite octahedra are the most common habit and typically exhibit small cube-faced step growths; however, other more complex habits occur. Colorless quartz associated with this occurrence exhibits quartzoid and rarely pseudo-cubic habits that have been of considerable interest to collectors of micromount specimens. The potential for gemstone and specimen-grade amethyst from this area is good.