How to identify Epidote

To correctly identify Epidote (Epidote), 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 pistachio-green to yellowish-green, but can also be dark green, brownish-green, or black. The green color is often diagnostic.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous (glassy) to resinous on crystal faces, sometimes dull in massive forms.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Can be crystalline (prismatic, often striated), granular, fibrous, or massive.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Prismatic crystals, often elongated and tabular, with characteristic striations parallel to the length. Crystals are typically monoclinic. Can also be found as radiating aggregates or granular masses.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Perfect cleavage on {001} and good cleavage on {100}, often visible as parallel lines or steps on crystal faces.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Common in regionally metamorphosed rocks (e.g., greenschist, amphibolite facies), contact metamorphic rocks (skarns), hydrothermally altered igneous rocks, and veins.

Key Facts

Hardness

6 - 7 on the Mohs scale

Specific Gravity

3.3 - 3.5 (relatively dense)

Crystal System

Monoclinic

Color

Pistachio-green, yellowish-green, dark green, brownish-green, black

Luster

Vitreous to resinous

Transparency

Transparent to translucent to opaque

Fracture

Uneven to conchoidal

Cleavage

Perfect on {001}, good on {100}

Composition

Calcium aluminum iron sorosilicate

Physical characteristics

• Crystal Habit: Prismatic, often elongated and tabular, commonly striated parallel to the length; also granular, fibrous, massive, or radiating aggregates.
• Cleavage Type: Perfect basal cleavage on {001} and good prismatic cleavage on {100}. Cleavage planes are often visible.
• Fracture Type: Uneven to conchoidal. Breaks with irregular, shell-like surfaces.
• Tenacity: Brittle. Easily breaks or crumbles under pressure.
• Luster Type: Vitreous (glassy) to resinous on crystal faces; can be dull in massive forms.

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