Quartz

specimen number:
2133268

location:
Llano, Llano Co., Texas, USA

description:
A neat locality example, this a double terminated partly gemmy reddish crystal of quartz on matrix. In good condition.

The pegmatite deposits of Llano County, Texas, located within the uplifted Precambrian core of the Llano Region, are world-renowned for their complex mineralogy and rare-earth element concentrations. Geologically, these granitic pegmatites intruded the surrounding metamorphic rocks, such as the Packsaddle Schist, approximately 1.1 billion years ago during the late stages of the Grenville Orogeny. The most famous locality, Baringer Hill, was a massive, zoned pegmatite uniquely rich in rare minerals like gadolinite, fergusonite, and cyrtolite, along with massive quartz and microcline feldspar. Historically, commercial interest in the area spiked in the late 19th century after the discovery of yttrium-bearing minerals, which were used for early industrial lighting filaments. The Nernst Lamp Company operated the Baringer Hill mine from the 1880s until around 1910, marking one of the earliest focused rare-earth mining efforts in the United States. While several other quarries produced industrial feldspar and quartz throughout the mid-20th century, many significant sites, including Baringer Hill, were eventually submerged under Lake Buchanan in 1937 following the completion of the Buchanan Dam. Today, the area remains a landmark for geological study, representing a rare example of a highly evolved Proterozoic pegmatite system.

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