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noun\ˈplā-j(ē-)ə-ˌklās, ˈpla-, -ˌklāz\
Definition of PLAGIOCLASE
: a triclinic feldspar; especially: one having calcium or sodium in its composition
Origin of PLAGIOCLASE
Greek plagios oblique + klasis breaking, from klan to break — more at clast
First Known Use: circa 1868
Any member of the series of abundant feldspar minerals that usually occur as light- to medium-grey-coloured, transparent to translucent grains or crystals. Plagioclase ranges in composition from albite to anorthite. It is used in the manufacture of glass and ceramics; iridescent varieties are valued as gemstones. The primary importance of plagioclase, however, derives from its role as a rock-forming mineral.