atomic number 14, silicon, Si - a tetravalent nonmetallic element; next to oxygen it is the most abundant element in the earth's crust; occurs in clay and feldspar and granite and quartz and sand; used as a semiconductor in transistors

orthoclase - a white or colored monoclinic feldspar

oligoclase, plagioclase - any of a rock-forming series of triclinic feldspars

moonstone - a transparent or translucent gemstone with a pearly luster; some specimens are orthoclase feldspar and others are plagioclase feldspar

spar - any of various nonmetallic minerals (calcite or feldspar) that are light in color and transparent or translucent and cleavable