It is a feldspathic semi-abrasive mineral consisting of clay, mica, feldspar and silica (Moh hardness of 5). It is a product of the hydro thermal alteration of intrusive rhyolite and is mined from a substantial deposit in the Mojave Desert of California. In a ceramic casting slip or plastic clay body, PV Clay has the unique capability of promoting plasticity from the clay portion, fluxing action from the feldspar portion, and low shrinkage and stability from the non-plastic quartz portion. Its relatively high potash and soda content give P. V. Clay a lower PCE than most kaolins and ball clays (18 vs. 26-35), and thus was widely used in the ceramic industry as a low temperature flux for artware and tile bodies. Its formula is quite similar to Cornwall Stone.