Any of a series of triclinic feldspars that form rocks WordNet 3.0 & Open English WordNet

Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. Wikipedia

Plagioclase is a series of tectosilicate minerals within the feldspar group. Wikipedia

A solid solution series of minerals in the feldspar group Wikipedia Disambiguation

Feldspars, albite - anorthite solid solution series Wikidata

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. Wiktionary

Any of a group of aluminum silicate feldspathic minerals ranging in their ratio of calcium to sodium. Wiktionary

Group of feldspar minerals. Wiktionary (translation)