a plagioclase feldspar whose composition corresponds to 70 to 90 percent albite
Origin of oligoclaseGerman oligoklas ; from Classical Greek oligos (see oligo-) + klasis, a fracture (see clastic), in contrast to orthoclase, because cleavage differs slightly from 90°
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.
Origin of oligoclaseoligo– + Greek klasis, cleavage (from klān, to break; see plagioclase feldspar).
(usually uncountable, plural oligoclases)
- (mineralogy) 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.
From oligo- +"Ž clase