PETROLOGIC RECONNAISSANCE OF MAFIC SCHIST FROM SOUTHWESTERN VIRGINIA: A SEARCH FOR SOAPSTONE

A small body of mafic schist in the western Virginia Piedmont less than a mile north of Ridgeway, VA was examined to determine its mineralogy and suitability for economic development. The rock outcrops on a low rise in a pasture and is cut by a creek.

Samples of mafic schist were collected and thin sections were made for petrographic analysis. Chlorite and amphibole are the major minerals in the mafic schist and talc is less abundant. Medium-coarse grained ( 0.7 to 1.9 mm) amphibole is enclosed in a medium-grained ( 0 .3mm to 0.6 mm) matrix of light green chlorite and colorless talc ( 0.2mm to 0.5 mm). Some larger (up to 3-5 mm)talc grains were seen in hand sample. Proportions of amphibole and chlorite vary, but talc is always subordinate in abundance. A few grains of plagioclase were noted in one sample.

In thin section at least three different amphiboles are apparent. Actinolite is pleochroic (X = very light green, Z = moderate-light blue-green). It exhibits high relief and low 3rd order interference colors. Extinction angles are generally about 16 degrees. Clear actinolite overgrows a amphibole with similar optical properties (X = colorless,

Z = moderate-light olive-green, low 2nd order colors), but with numerous very fine-grained inclusions of a very high relief phase (sphene ? rutile ?). A third colorless acicular amphibole forms overgrowths on actinolite and may be cummingtonite (extinction angle ~15 degrees) . Chlorite pleochroism varies from very light green-almost colorless to light green.

Based on the low abundance of talc and high proportion of chlorite and amphibole, the rock is best termed a talc-bearing chlorite amphibole schist rather than a soapstone. The low talc content and the abundance of chlorite and amphibole make this rock unsuitable for use a talc ore or as a carving material. The rock is still easily cut and such chlorite schists are commonly quarried privately or for local consumption (counter tops, tiling, etc.). The body therefore could hold some economic value based on this initial investigation of ground level float and outcropping and warrants further investigation.