oligoclase

A white, gray, green or red variety of plagioclase feldspar that contains a higher proportion of sodium than calcium and is common in silica-rich igneous rocks.

A soda-lime triclinic feldspar, the soda predominating. See feldspar.

A triclinic soda-lime feldspar. See feldspar.

A plagioclase feldspar, the second member of the Albite-Anorthite solid solution series. Primarily found as small crystals in impure marble. Oligoclase contains a small amount of calcium substituting for some of the sodium in its formula. Oligoclase with reddish-golden inclusions found in Norway and Canada is called sunstone.

any of a series of triclinic feldspars that form rocks