Topaz, an aluminum fluorosilicate with the formula Al2SiO4(F,OH)2 is found in a number of Colorado localities. The Tarryall area in Park County is known for the striking topaz specimens discovered there. Topaz, with a hardness of 8 on the Mohs scale, is a gem mineral harder than quartz. Topaz in the Tarryall Mountains forms in miarolitic cavities in pegmatites (coarse-grained granite). The China Wall, a granitic cupola in the Tarryall area, also yields topaz.
East of the China Wall, the Mutakat Road (Forest Road 211) winds its way near an area where a number of claims have been producing gem topaz for several years. The Hayman fire of 2002, the largest fire in Colorado's history, has been a major factor in the discovery of new topaz in the area. Frequent rain storms form newly eroded gullies that uncover topaz-bearing pegmatites. Mountain rains have also revealed many topaz and quartz crystals on the surface. Rich Fretterd, a member of the Lake George Gem and Mineral Club, staked the Petra placer in April 2004 after he discovered a number of fine topaz specimens at this locality. The name of the claim comes from the Latin petra, meaning rock or stone. The Petra placer is southeast of Pilot Peak (SW1/4 NE1/4 sec. 12 T11S R72W).
Fretterd is presently working on topaz-bearing pegmatites that are part of the Redskin Granite, a zoned, oval-shaped intrusion covering approximately 49 km'. The Redskin Granite, a late stage variant of the Pikes Peak Granite, intrudes the western part of the Pikes Peak batholith. Pikes Peak Granite weathers pink, whereas the Redskin Granite weathers red because of the oxidation of iron-rich micas. The Redskin Granite is also known for its topaz-bearing pegmatites concentrated within and near the contact with Pikes Peak Granite.
The specimens from the Petra placer are remarkable for their size and clarity. Many specimens have a bluish tinge. The specimen shown in Figure 1 was found loose, just below the surface in an alluvial-colluvial deposit. The slightly abraded specimen had been transported a short distance from the crystal-bearing pegmatite. This topaz specimen has a blocky, prismatic crystal habit with some of the prism faces slightly etched. The pale-blue crystal has a transparent interior and is terminated at one end—the other end is the cleavage plane.
New specimens continue to be found. Anhedral specimens are faceted into gems, whereas euhedral specimens make their way into museums or the mineral cabinets of rock hounds. The Petra placer is now a significant Colorado topaz locality.
Figure 1: Topaz specimen from the Petra placer. This prismatic crystal specimen terminates with a frosted pyrmaid on top. Rich Fretterd specimen, Steven Veatch photograph.
×Figure 1: Topaz specimen from the Petra placer. This prismatic crystal specimen terminates with a frosted pyrmaid on top. Rich Fretterd specimen, Steven Veatch photograph.
pp. 12
26th Annual New Mexico Mineral Symposium
November 12-13, 2005, Socorro, NM
Print ISSN: 2836-7294 Online ISSN: 2836-7308
