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.
A plagioclase feldspar whose composition corresponds to 70 to 90 percent albite.
A white to gray triclinic mineral of the plagioclase feldspar group. Oligoclase occurs in igneous rocks with a relatively high silica content, such as granite. Chemical formula: (Na,Ca)(Al,Si)AlSi2O8.
(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.
Origin of oligoclase
- oligo– Greek klasis cleavage (from klān to break plagioclase feldspar)
From American Heritage Dictionary of the English Language, 5th Edition
- From oligo- +"Ž clase