Oligoclase vs. Plagioclase

Oligoclase and Plagioclase Definitions
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.
Plagioclase
(mineral) Any of a group of aluminum silicate feldspathic minerals ranging in their ratio of calcium to sodium.
Oligoclase
(mineral) 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.
Plagioclase
A general term used of any triclinic feldspar. See the Note under Feldspar.
Oligoclase
A triclinic soda-lime feldspar. See Feldspar.
Plagioclase
Any of a rock-forming series of triclinic feldspars
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Oligoclase
Any of a rock-forming series of triclinic feldspars