How to identify Actinolite Schist

To correctly identify Actinolite Schist (Actinolite), check each of these features in order. Many rocks and minerals look alike, so cross-reference multiple properties before deciding.

Step-by-step identification

1. 1

   Color

   Overall color and any zoning or banding

   Typically light to dark green, grayish-green, or sometimes blackish-green.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Often silky or vitreous on cleavage surfaces, dull on fractured surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Strongly foliated (schistose) with visible, elongated, often needle-like or fibrous actinolite crystals aligned parallel. Can feel slightly greasy or soapy due to chlorite.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Actinolite crystals are typically acicular (needle-like), prismatic, or fibrous. In schist, they are usually elongated and aligned.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Actinolite itself has two perfect cleavages at approximately 56 and 124. The schistosity of the rock represents a pervasive planar fabric, not individual mineral cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in regional metamorphic terrains, particularly in areas that experienced greenschist facies metamorphism of mafic protoliths. Common in orogenic belts and ancient shield areas.

Key Facts

Hardness

5.5-6 on Mohs scale (for actinolite mineral)

Specific Gravity

3.0-3.2 (for actinolite mineral)

Crystal System

Monoclinic (for actinolite mineral)

Color

Green, grayish-green, dark green

Luster

Silky, vitreous, dull

Transparency

Translucent to opaque

Fracture

Uneven to splintery

Cleavage

Perfect on {110} at 56 and 124 (for actinolite mineral)

Composition

Hydrous calcium magnesium iron silicate (Ca2(Mg,Fe)5Si8O22(OH)2)

Physical characteristics

• Crystal Habit: Acicular, prismatic, fibrous, bladed (for actinolite mineral)
• Cleavage Type: Perfect prismatic (for actinolite mineral)
• Fracture Type: Uneven to splintery
• Tenacity: Brittle (for non-asbestiform actinolite); flexible (for asbestiform actinolite)
• Luster Type: Silky to vitreous

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