to occur at the lowest topographic elevations. Where the Cretaceous rocks rim the Llano uplift, a sharp topographic rise or escarpment is common. Central Mineral region The Llano Uplift region is also called the Central Mineral region of Texas because of the occurrence of the great variety of minerals found in and the numerous ore prospecting pits dug into exposed Precambrian rocks and Lower Paleozoic strata. Over the decades, a few small mines have yielded yttrium and other rare-earth minerals, magnetite, feldspar, vermiculite, serpentine, and gem quality topaz. Briefly, galena as lead ore was mined from limestone lying unconformably upon granite knobs that were once hills before being submerged by rising relative sea level in the Cambrian. Minor showings of gold, silver, copper, tin, bismuth, molybdenum, tungsten, and uranium minerals have been found and explored in prospecting pits. Before it closed in 1980, the Southwestern Graphite mine northwest of Burnet, Texas, was the only major producer of high-purity graphite in North America for several decades. In the past large quantities of soapstone were excavated from outcrops south of Llano, Texas, and ground for use as insecticide carrier and inert filler in various products. The principal mineral resources currently produced from Central Mineral region consist of fracturing sand (“Frac sand”), crushed stone, and building stone. Granite has been quarried from almost innumerable localities and the active production of dimension stone continues today from a dome of coarse pink Town Mountain Granite near Marble Falls, Texas. See also Geology of Texas Notes Geologic provinces of Texas Geologic domes Rock formations of Texas Landforms of Llano County, Texas