Oligoclase n. : A triclinic soda-lime feldspar. See Feldspar.

Example:


Taxonomy
Oligoclase, free encyclopedia, albite, shades of grey, orthoclase, anorthite, mineral, sodium feldspar, presence, search, Crown Point, Essex County, New York, New York, United States, United States of America, rock, belonging, chemical composition, crystallographic.

Defination from the web:
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. ... Oligoclase occurs, often accompanying orthoclase, as a constituent of plutonic igneous rocks such as ... The distinctive texture of rapakivi granite is due to oligoclase rims on orthoclase phenocrysts. ...