Chemical Classification

Silicate

Color

Usually white, pink, gray or brown. Also colorless, yellow, orange, red, black, blue, green.

Streak

White

Luster

Vitreous. Pearly on some cleavage faces.

Diaphaneity

Usually translucent to opaque. Rarely transparent.

Cleavage

Perfect in two directions. Cleavage planes usually intersect at or close to a 90 degree angle.

Mohs Hardness

6 to 6.5

Specific Gravity

2.5 to 2.8

Diagnostic Properties

Perfect cleavage, with cleavage faces usually intersecting at or close to 90 degrees. Consistent hardness, specific gravity and pearly luster on cleavage faces.

Chemical Composition

A generalized chemical composition of X(Al,Si)4O8, where X is usually potassium, sodium, or calcium, but rarely can be barium, rubidium, or strontium.

Crystal System

Triclinic, monoclinic

Uses

Crushed and powdered feldspar are important raw materials for the manufacture of plate glass, container glass, ceramic products, paints, plastics and many other products. Varieties of orthoclase, labradorite, oligoclase, microcline and other feldspar minerals have been cut and used as faceted and cabochon gems.