logo

Video encyclopedia

Orthoclase

1:17

Potassium feldspar (orthoclase)

1:36

All you want to know about Orthoclase Stone

1:45

Orthoclase: The mineral Orthoclase information and pictures

3:10

Orthoclase under microscope

3:50

Ruby, Orthoclase, and Emerald

Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture," because its two cleavage planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar. The gem known as moonstone (see below) is largely composed of orthoclase.