Crystal Anhydrite

Chemical Formula

CaSO₄

Composition

Calcium sulfate

Color

Colorless, white, yellow, gray, blue, orange-red, red, pink, purple.

Streak

White to light gray

Hardness

3 - 3.5

Crystal System

Orthorhombic

Crystal Forms 
and Aggregates

Individual crystals, which are tabular and prismatic, are uncommon. Often fibrous, in parallel veins that break off into cleavage fragments, and as fan-like groupings. Also grainy, massive, nodular, as rectangular cleavage fragments, and as easily cleavable crystal groupings.

Transparency

Transparent to translucent

Specific Gravity

2.9 - 3.0

Luster

Vitreous to pearly

Cleavage

2,3 - forming a cube

Fracture

Uneven to splintery

Tenacity

Brittle

Other ID Marks

Many specimens are fluorescent.

Complex Tests

Specimens that are not fluorescent may become fluorescent after heating.

In Group

Sulfates; Anhydrous Sulfates

Striking Features

Cleavage properties, crystal habits, and low specific gravity.

Environment

In sedimentary rock layers, in salt domes, and in igneous traprock.
 

Rock Type

Igneous, Sedimentary

Popularity (1-4)

2

Prevalence (1-3)

3

Demand (1-3)

1