How to identify Unakite

To correctly identify Unakite (Unakite (altered granite)), 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

   Distinctive mottled or speckled appearance with shades of pistachio-green (epidote), pink to reddish-orange (orthoclase feldspar), and colorless to grey (quartz).

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

   Vitreous to sub-vitreous for quartz and feldspar; epidote can be vitreous to resinous.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granular, phaneritic (coarse-grained), interlocking crystalline texture, characteristic of a granitic rock.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Individual mineral grains are anhedral to subhedral, forming an interlocking mosaic. Epidote may show prismatic habit within the rock.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Orthoclase feldspar exhibits two distinct cleavages at approximately 90 degrees. Epidote has one perfect cleavage. Quartz has no cleavage.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Found in areas where granitic intrusions have undergone hydrothermal alteration, often associated with regional metamorphism or fault zones where fluid flow is concentrated.

Key Facts

Hardness

6-7 on Mohs scale (due to quartz and feldspar, epidote is 6-7)

Specific Gravity

2.8-3.2 (varies with mineral proportions, epidote is denser)

Crystal System

Monoclinic (epidote), Triclinic (orthoclase), Hexagonal (quartz) - as a rock, it's an aggregate of these systems

Color

Green (epidote), pink/red (orthoclase), colorless/grey (quartz)

Luster

Vitreous to sub-vitreous

Transparency

Opaque to translucent

Fracture

Conchoidal (quartz), uneven to splintery (feldspar, epidote)

Cleavage

Good in feldspar (2 directions at ~90°), perfect in epidote (1 direction), none in quartz

Composition

Primarily epidote, orthoclase feldspar, and quartz. Minor accessory minerals may be present.

Physical characteristics

• Crystal Habit: Granular, massive aggregate of anhedral to subhedral crystals.
• Cleavage Type: Feldspar: two distinct cleavages at nearly 90 degrees. Epidote: one perfect basal cleavage. Quartz: no cleavage.
• Fracture Type: Conchoidal (quartz), uneven to splintery (feldspar, epidote).
• Tenacity: Brittle.
• Luster Type: Vitreous to sub-vitreous.

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