How to identify Unakite

To correctly identify Unakite (Unakite (altered granite composed of epidote, pink orthoclase feldspar, and quartz)), 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 pattern of pistachio green (epidote), pink (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, resinous to vitreous for epidote.

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granular, interlocking crystalline texture, characteristic of an altered igneous rock. Grain size can vary from fine to coarse.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Individual mineral grains (epidote, orthoclase, quartz) are anhedral to subhedral within the rock matrix.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

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

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed in areas where granitic rocks have undergone hydrothermal alteration or low-grade regional metamorphism, often associated with fault zones or areas of fluid flow.

Key Facts

Hardness

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

Specific Gravity

2.85 to 3.20 (variable depending on mineral proportions, epidote is denser).

Crystal System

Monoclinic (epidote, orthoclase), Trigonal (quartz). Unakite as a rock does not have a single crystal system.

Color

Pistachio green, pink, and colorless/grey.

Luster

Vitreous to sub-vitreous.

Transparency

Opaque to translucent.

Fracture

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

Cleavage

Good in orthoclase (two directions at ~90°), perfect in epidote (one direction), absent in quartz.

Composition

Primarily epidote (Ca2(Al,Fe)3(SiO4)3(OH)), orthoclase feldspar (KAlSi3O8), and quartz (SiO2).

Physical characteristics

• Crystal Habit: Granular, massive, anhedral to subhedral crystals within a rock matrix.
• Cleavage Type: Good in orthoclase (prismatic), perfect in epidote (basal), absent in quartz.
• Fracture Type: Conchoidal (quartz), uneven to splintery (feldspar, epidote).
• Tenacity: Brittle.
• Luster Type: Vitreous to sub-vitreous.

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