Characteristic Fluorescence (short wave) of Scheelite in limestone with garnets, hematite, calcite, epidote Location: not specifically listed, but assume to be in the Quitman Mountains associated with an often noted skarn (intrusive contact with host limestone). Chemical formula: Ca(WO4) Crystal system: Tetragonal Left Specimen size: 7 x 5.5 x 3.5 centimeters Right Specimen size: 12 x 4.5 x 5 cm Left Specimen weight: 237 grams Right Specimen weight: 521 grams Collection reference: TMM 701 Additional Information: "The tungsten-bearing mineral scheelite has been known since 1916 in recrystallized sugary limestone beds of the Torcer Formation where it has been metamorphosed on the west side of the Quitman pluton and west of a line projected along the Bonanza fissure (Udden, 1941). According to a report by J. F. McAllister (written commun., 1942), the scheelite is in isolated grains, coarse aggregates, and thin veinlets replacing the limestone. Kock discontinuously mineralized with tungsten was traced for about 700 feet along the contact zone. The principal minerals associated with the scheelite are specular hematite, garnet, epidote, tremolite, pyrite, quartz, calcite, and secondary copper minerals." (from "Geology of the Sierra Blanca Area, Hudspeth County, Texas" Albritton & Smith, USGS Professional Paper 479, 1965.)
Serpentinite, a building or decorative stone composed of one or more serpentine minerals (in this case Antigorite) Locality: Coal Creek Serpentine Prospect, north Gillespie County, Texas Mineralogy: > 90% antigorite, ~4% opal, 1-2% magnetite, lesser amounts of chromite, pyrite, calcite Crystal System: Antigorite is monoclinic Specimen size: 4 in x 2.5 in x 1 in thick Specimen weight: 280 grams In the BEG hand sample collection. Additional Information: Virgil Barnes, et al. assessed the PreCambrian Serpentinite deposits around the Llano Uplift in 1950 and provided the mineralogy above (BEG Pub. #5020). They mapped the Coal Creek serpentine mass at 3.7 miles long and ranging from 0.3 to about 1.4 miles wide. It's been reported that serpentinite from this area has been used for terrazzo chips.
Location: listed as being from 1 mile north of Mica Tanks, in the Plato Verde Prospect, Van Horn Mountains County: Culberson County, Texas Minerals: assume disseminated Cerargyrite (synonym for Chlorargyrite) from the mine description text below. Chemical Formula: AgCl Crystal system: Isometric (typically clear when fresh with waxy, adamintine luster) Specimen size: 6 x 3 x 1.5 inches Specimen weight: 690 grams Collection Reference: TMM 1310 In the Jackson School of Geosciences Collection, at the University of Texas at Austin. Additional Information: Very specific information on this mine is found on the Supporting Text on the Geologic Quadrangle Map No. 23, Geology of the Van Horn Mountains, By Page C. Twiss, August 1959. "The Plata Verde mine, a mile northwest of the Mica Mine area along the western base of the Van Horn Mountains, contains small quantities of cerargyrite (horn silver). The mine was worked sporadically during the 1930's and 1940's. Most of the production occurred between 1936 and 1939, when 10,800 tons of ore were shipped to the El Paso smelter of American Smelting and Refining Company. The silicious silver chloride ore contained 9 to 26 ounces of silver and 0.23 to 0.46% copper, 68% silica, 13% alumina, 2% ferric iron oxide, 1% lime, 0.1% zinc, and 0.3% sulfur. The most recent exploratory work was done during 1951-1955, when a vertical shaft was sunk at the south end of the old workings (Peter T. Flawn, personal communication). According to Flawn, the mineralization is controlled by at least two major north trending gravity faults which border the shafts and inclines on the east and west. Small blebs of cerargyrite are concentrated along bedding planes and shear zones (parallel to the bedding) in the steeply dipping muscovite sandstone beds of the Permian Powwow conglomerate in the Wolfcamp Series."
