orthoclase


orthoclase

/

Orthoclase from Serra de Peneda, Portugal—Emil Javorsky/EB Inc.

Common alkali feldspar mineral, potassium aluminosilicate (KAlSiO), that usually occurs as variously coloured grains in granite. Orthoclase is used in the manufacture of glass and ceramics; occasionally, transparent crystals are cut as gems. It is primarily important as a rock-forming mineral, however, and is abundant in igneous rocks, pegmatites, and gneisses. The feldspar minerals consist of sodium, potassium, and calcium aluminosilicates, and any feldspar may be chemically classed by the percentage of each of these three pure compounds, called end-members. Orthoclase is the potassium-bearing end-member of the system. Microcline is a lower temperature structural form of the same chemical composition as orthoclase.

This entry comes from Encyclopædia Britannica Concise.
For the full entry on orthoclase, visit Britannica.com.

Seen & Heard

What made you look up orthoclase? Please tell us what you were reading, watching or discussing that led you here.

Get Our Free Apps
Voice Search, Favorites,
Word of the Day, and More
Join Us on FB & Twitter
Get the Word of the Day and More