How to identify Serpentinite

To correctly identify Serpentinite (Serpentinite (metamorphic rock composed of serpentine minerals)), 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 various shades of green (light to dark green, yellowish-green, bluish-green), often mottled or veined with black, white, or reddish-brown.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Greasy, waxy, silky (especially fibrous varieties like chrysotile), or dull.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Smooth, slippery, fibrous, or granular. Often feels soapy to the touch. Can be massive, foliated, or schistose.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Serpentine minerals typically form microscopic to macroscopic aggregates. Antigorite and lizardite are platy or massive, while chrysotile is fibrous.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Serpentine minerals generally have good to perfect cleavage in one direction (basal), but in massive serpentinite, it may not be apparent. Fibrous chrysotile exhibits excellent fibrous parting.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in areas of oceanic crust and upper mantle that have undergone hydration, such as mid-ocean ridges, subduction zones, and obducted ophiolite complexes. Often associated with fault zones and shear zones.

Key Facts

Hardness

2.5-4 (Mohs scale)

Specific Gravity

2.5-2.9 g/cm

Crystal System

Monoclinic (antigorite, lizardite), Orthorhombic (chrysotile)

Color

Green, yellowish-green, brownish-green, blackish-green

Luster

Greasy, waxy, silky, dull

Transparency

Translucent to opaque

Fracture

Conchoidal to splintery (fibrous varieties)

Cleavage

Good to perfect basal cleavage in individual serpentine minerals, but often not visible in massive rock. Fibrous chrysotile exhibits excellent fibrous parting.

Composition

Hydrous magnesium silicate, primarily composed of serpentine group minerals (Mg3Si2O5(OH)4)

Physical characteristics

• Crystal Habit: Massive, platy, fibrous, lamellar, or granular aggregates.
• Cleavage Type: Good to perfect basal cleavage (001) in individual serpentine minerals, but often obscured in rock masses.
• Fracture Type: Conchoidal, splintery (fibrous varieties), or uneven.
• Tenacity: Flexible, sectile (chrysotile), or brittle.
• Luster Type: Greasy, waxy, silky, dull.

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