Crystal Actinolite

Chemical Formula

Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂

Composition

Basic calcium, magnesium, iron silicate

Color

Light to dark green; grayish green to black.

Streak

Colorless

Hardness

5.5 - 6

Crystal System

Monoclinic

Crystal Forms 
and Aggregates

As elongated prismatic crystals, in bladed groups, columnar, fibrous, reticulated and acicular. Also occurs radiating, as wheat sheaf formations, as thin hairlike masses, and as tough interlocking fibers which may appear massive.

Transparency

Translucent; rarely transparent.

Specific Gravity

2.9 - 3.5

Luster

Vitreous, silky

Cleavage

2,2 - prismatic

Fracture

Uneven, splintery

Tenacity

Brittle. Fibrous forms are elastic.

Complex Tests

Insoluble in acid

In Group

Silicates; Inosilicates; Amphibole Group

Striking Features

Green color, crystal habit, and cleavage angle of amphiboles.

Environment

In contact and regional metamorphic rocks, Serpentine deposits, hydrothermal replacement deposits, and as a secondary mineral in igneous basalt and diabase.

Rock Type

Igneous, Metamorphic

Popularity (1-4)

2

Prevalence (1-3)

2

Demand (1-3)

1