How to identify Serpentinite

To correctly identify Serpentinite (Serpentinite (a metamorphic rock composed of serpentine group 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 dark green, yellowish-green, olive green, brownish-green, or black; often mottled or variegated.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

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

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Massive, fibrous, platy, or granular. Often feels smooth or soapy to the touch. Can exhibit a 'snake-skin' like pattern.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Serpentine minerals are typically cryptocrystalline or microcrystalline, forming aggregates. Fibrous varieties (chrysotile) can show delicate, flexible fibers. Platy varieties (antigorite, lizardite) form fine-grained masses.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Serpentine minerals generally have one perfect cleavage (basal), but in massive serpentinite, this is rarely observed as distinct planes due to the fine-grained, interlocking nature of the aggregates. Fibrous chrysotile shows excellent cleavage parallel to the fiber length.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Associated with ophiolite complexes (fragments of oceanic crust and upper mantle obducted onto continental margins), subduction zones, and major fault zones where ultramafic rocks have been hydrated. Also found in metamorphic terrains where peridotites have undergone hydrothermal alteration.

Key Facts

Hardness

2.5-4 on the Mohs scale (for serpentine minerals).

Specific Gravity

2.5-2.8 g/cm³.

Crystal System

Monoclinic (antigorite, chrysotile) or Orthorhombic (lizardite). Serpentinite as a rock is massive or aggregate, not a single crystal.

Color

Dark green, yellowish-green, olive green, brownish-green, black; often mottled.

Luster

Greasy, waxy, silky (fibrous varieties), dull.

Transparency

Translucent to opaque.

Fracture

Conchoidal to splintery or uneven.

Cleavage

Perfect basal cleavage in individual serpentine minerals, but rarely observed in massive rock.

Composition

Hydrous magnesium iron phyllosilicate (Mg,Fe)₃Si₂O₅(OH)₄, with varying proportions of antigorite, lizardite, and chrysotile.

Physical characteristics

• Crystal Habit: Massive, platy, fibrous, or granular aggregates. Individual serpentine minerals are typically microcrystalline.
• Cleavage Type: Perfect basal cleavage (001) in individual serpentine minerals, but generally not visible in the rock.
• Fracture Type: Conchoidal, splintery, or uneven.
• Tenacity: Brittle to flexible (chrysotile asbestos).
• Luster Type: Greasy, waxy, silky, dull.

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