mineral

Actinolite

Ca2(Mg,Fe)5Si8O22(OH)2

Hardness: 5-6 (Mohs); Color: Dark green to grayish-green; Luster: Vitreous to silky; Crystal structure: Monoclinic; Cleavage: Perfect in two directions; Specific gravity: 3.0-3.4

Hardness: 5-6 (Mohs)
Color: Dark green to grayish-green
Luster: Vitreous to silky

Identified May 23, 2026More mineral →

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Physical properties

Hardness: 5-6 (Mohs); Color: Dark green to grayish-green; Luster: Vitreous to silky; Crystal structure: Monoclinic; Cleavage: Perfect in two directions; Specific gravity: 3.0-3.4

Formation & geological history

Formed through low-grade metamorphism of magnesium-rich rocks (such as basalt or dolostone) in regional metamorphic belts, often associated with greenschist facies.

Uses & applications

Primarily used as a mineral specimen for collectors; historically used in some forms of industrial asbestos insulation (specifically the fibrous variety), though this is now uncommon due to health risks.

Geological facts

The fibrous form of actinolite is one of the six types of minerals commonly referred to as 'asbestos.' Its name is derived from the Greek word 'aktinos,' meaning ray, referring to the radiated nature of its crystals.

Field identification & locations

Identify in the field by its distinctive green color, needle-like or bladed crystal habit, and the 120-degree angle between cleavage planes typical of amphiboles. Commonly found in metamorphic terrains like the Alps or the California Coast Ranges.