Serpentinite, Gillespie County, Texas
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.