How to identify Chlorite Schist

To correctly identify Chlorite Schist (Chlorite Schist), 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), often with a dull to slightly greasy luster.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Dull to sub-vitreous, sometimes greasy or pearly on cleavage surfaces.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Schistose, fine- to medium-grained, with visible platy minerals (chlorite) aligned, giving it a foliated appearance. Can feel slightly soapy or slippery due to chlorite.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Chlorite crystals are typically anhedral to subhedral, forming platy aggregates that define the schistosity. Other minerals like quartz and albite are granular.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Excellent schistosity, allowing the rock to split easily into thin, irregular sheets or plates along the planes of chlorite alignment.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in regional metamorphic terrains, particularly in ancient mountain belts and subduction zones, where mafic igneous or argillaceous sedimentary rocks have undergone greenschist facies metamorphism.

Key Facts

Hardness

2-2.5 (Mohs scale, due to chlorite)

Specific Gravity

2.6-3.0 g/cm

Crystal System

Monoclinic (for chlorite minerals)

Color

Green (light to dark)

Luster

Dull to sub-vitreous, greasy, or pearly

Transparency

Opaque to translucent (thin flakes)

Fracture

Uneven to splintery, parallel to foliation

Cleavage

Excellent schistosity (rock property), perfect basal cleavage (chlorite mineral)

Composition

Dominated by chlorite group minerals, with variable amounts of quartz, albite, epidote, actinolite, and sometimes garnet, magnetite, or pyrite.

Physical characteristics

• Crystal Habit: Chlorite typically forms platy, pseudohexagonal crystals or aggregates, often intergrown with other minerals.
• Cleavage Type: The rock exhibits excellent schistosity, allowing it to split along planes defined by aligned chlorite. Individual chlorite crystals have perfect basal cleavage {001}.
• Fracture Type: Uneven to splintery, often controlled by the schistosity.
• Tenacity: Flexible in thin flakes (chlorite), but the rock itself is brittle across the foliation.
• Luster Type: Dull to sub-vitreous, sometimes greasy or pearly on cleavage surfaces.

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