How to identify Unakite

To correctly identify Unakite (Unakite (Epidote, Feldspar, 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

   Mottled green (epidote), pink to reddish-orange (potassium feldspar), and colorless to greyish (quartz). The green is typically the most dominant and characteristic color.

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, phaneritic (coarse-grained) to medium-grained, with interlocking crystals. The texture is typically massive, lacking foliation.

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. Epidote may sometimes show prismatic habits within the rock.

5. 5

   Cleavage

   How it breaks: flat cleavage planes vs irregular fracture

   Potassium feldspar exhibits two distinct cleavages at approximately 90 degrees. Epidote has one perfect cleavage. Quartz has no cleavage but exhibits conchoidal fracture.

6. 6

   Geological Environment

   The rock formation and setting where it occurs

   Formed from the hydrothermal alteration (epidotization) of granitic rocks. This typically occurs in areas of low-grade regional metamorphism, contact metamorphism, or along fault zones where hydrothermal fluids have circulated through pre-existing granites. It is often found in association with other metamorphic rocks and altered igneous intrusions.

Key Facts

Hardness

6-7 on the Mohs scale (due to quartz and epidote components).

Specific Gravity

2.8-3.2 (variable depending on mineral proportions, epidote is denser).

Crystal System

Monoclinic (epidote), Triclinic (plagioclase feldspar, if any remains), Monoclinic (orthoclase), Triclinic (microcline), Trigonal (quartz). As a rock, it does not have a single crystal system.

Color

Green (epidote), pink/reddish-orange (potassium feldspar), colorless/grey (quartz).

Luster

Vitreous to sub-vitreous.

Transparency

Opaque to translucent.

Fracture

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

Cleavage

Good in epidote (one direction), good in feldspar (two directions at ~90 degrees), absent in quartz.

Composition

Primarily composed of epidote, potassium feldspar (orthoclase or microcline), and quartz. Minor accessory minerals may include plagioclase feldspar (unaltered remnants), chlorite, magnetite, and zircon.

Physical characteristics

• Crystal Habit: Granular aggregate of anhedral to subhedral crystals. Epidote may show prismatic forms.
• Cleavage Type: Perfect in epidote (one direction), good in feldspar (two directions).
• Fracture Type: Conchoidal (quartz), uneven to splintery (epidote, feldspar).
• Tenacity: Brittle.
• Luster Type: Vitreous to sub-vitreous.

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