How to identify Unakite

To correctly identify Unakite (Unakite (Epidote-Feldspar rock)), 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

   Mottled green (epidote), pink (feldspar), and sometimes colorless/grey (quartz). The green is typically pistachio to yellowish-green, and the pink can range from salmon to reddish-pink.

2. 2

   Luster

   How the surface reflects light: metallic, vitreous, dull

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

3. 3

   Texture

   Grain size and surface feel: coarse, fine, glassy

   Granitic, medium to coarse-grained, interlocking crystalline texture.

4. 4

   Crystal Form

   Shape of visible crystals or crystal faces

   Individual mineral grains (epidote, feldspar, quartz) are anhedral to subhedral, forming an interlocking mosaic within the rock.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Feldspar exhibits two distinct cleavages at or near 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 been subjected to hydrothermal alteration, often associated with regional metamorphism or contact metamorphism near intrusive bodies, particularly in ancient mountain belts.

Key Facts

Hardness

6-7 (Mohs scale, due to constituent minerals: epidote 6-7, feldspar 6-6.5, quartz 7)

Specific Gravity

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

Crystal System

Monoclinic (epidote, feldspar), Trigonal (quartz) - refers to the individual minerals, not the rock as a whole

Color

Mottled green, pink, and grey/colorless

Luster

Vitreous to sub-vitreous

Transparency

Opaque to translucent

Fracture

Uneven to conchoidal (quartz), irregular (feldspar, epidote)

Cleavage

Good in feldspar (2 directions), perfect in epidote (1 direction), none in quartz

Composition

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

Physical characteristics

• Crystal Habit: Granular, massive, interlocking anhedral to subhedral crystals of constituent minerals.
• Cleavage Type: Good in feldspar (two directions at ~90°), perfect in epidote (one direction), absent in quartz.
• Fracture Type: Uneven to conchoidal (quartz), irregular (feldspar, epidote).
• Tenacity: Brittle.
• Luster Type: Vitreous to sub-vitreous.

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