Barringer Hill

Barringer Hill is a geological and mineralogical site in central Texas. It lies on the former west side of the Colorado river, beneath Lake Buchanan, about 22 miles (35 km) northeast of the town of Llano. The hill consists of a pegmatite and geologically, lies near the eastern edge of the Central Mineral Region in the Texas Hill Country. It is named for John Baringer, who discovered in it large amounts of gadolinite about 1887 (Hess).

The Barringer (Baringer) pegmatite was discovered in 1887 and, until its disappearance beneath the water of Lake Buchanan in 1937, was one of the most significant places in America from a mineralogical standpoint. Described by the United States Geological Survey as one of the greatest deposits of rare-earth minerals in the world, the pegmatite was the first place geologists discovered fergusonite, monofergusonite, thorogummite, yttrialite, and nivenite. The pegmatite is centrally located in the Lone Grove pluton, a 1.6 Ga old rapakavi granite, intruded into Valley Spring Gneiss. Geologic evidence suggests the pluton's emplacement as a rather shallow intrusion of magma, possibly in a sub-caldera type situation. An original depth of five to seven kilometers may be assumed for the present level of exposure (Denney). Prior to mining, the hill was described as 40 feet (12 m) tall by about 100 feet (30 m) wide and 250 feet (76 m) long. Hess describes the intrusion being surrounded by a graphic granite of peculiar beauty and definite structure, being more like a text-book illustration. A central quartz mass was described more than 40 ft (12 m) across, with distinct white bands, from one-eighth to one-half inch wide. Within the white bands were found fluid inclusions and bubbles that moved only slowly when the specimen was tilted. Between these bands the quartz is glassy and clear. At one place a vug was found large enough for a man to enter, lined with smoky quartz crystals reaching 1000 lb (500 kg) or more in weight. A large crystal of smoky quartz was removed that weighed over six hundred pounds (270 kg). It was 43 inches (1,100 mm) high and 28 inches (710 mm) broad and 15 inches (380 mm) thick (1090 by 710 by 380 mm). The feldspar consisted of an intergrowth of microcline and albite, of a brownish flesh color, and occurred in large masses reaching over 30 feet (9.1 m) in diameter (Hess).

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