CO-CRYSTALIZATION OF TOPAZ, RED BERYL, HEMATITE AND QUARTZ AT TOPAZ MOUNTAIN, JUAB COUNTY, UTAH

Topaz Mountain is well known to mineral collectors for the amber colored topaz on rhyolite. Crystals of red beryl in tabular hexagons, hematite in thin crystalline flakes, as well as quartz have grown along with the topaz. Late stage calcite and amethyst occur in some vesicles. Macroscopic and microscopic examination show that the principle minerals were probably all crystallizing at nearly the same time. One of the questions we are trying to answer is the origin of these crystals. Topaz Mountain is the mineral rich youngest rhyolite flow in the Thomas Range in western Utah. Vapor phase crystallization occurred as Si and Al along with Be were transported to open vesicles where crystals were formed. During fieldwork in 2003 (and previous years) samples were collected for examination at UWG. Many of the largest topaz crystals collected are 3.5 cm sandy crystals where euhedral crystals enclose “quartz sand”. Further microscopic examination will determine if they are the result of chemical (etching) or physical processes (inclusions). Similarly, the crystalline flakes of hematite appear not only on the exterior of topaz crystals, but also within the topaz crystals. Hematite’s crystallographic relationship to topaz is complex. The most common relationship is for ~10% of the hematite crystal to be included within a topaz crystal with the rest of the hematite projecting out as thin plates. Some of the hematite is completely inside the topaz as thin plates that are parallel to the cleavage direction (001). Rare topaz crystals have thin hematite plates that cover a pyramid face. Red beryl occurs both alone and in conjunction with topaz and hematite crystals. The largest samples are ~0.6cm diameter hexagonal prisms terminated by pinacoids with short 0.2cm prism faces. The red beryl is distinctly deep red in the center of the crystals fading to lighter shades of red to almost pink at the edges of the faces. The larger samples most often occur attached to rhyolite matrix, while smaller samples (~0.2cm diameter) occur adjoined to topaz crystal faces. In exceptional cases hematite flakes were included with the red beryl. These hematite crystals appear to grow perpendicular to the terminating pinacoid (0001) faces. Further evidence of the co-crystallization is given with the observation of small topaz on the face of some of the red beryl.