Unakite

Metamorphic Rock (specifically, an altered granite)

Unakite

Also known as: Epidote Granite

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Description

Unakite is a distinctive metamorphic rock characterized by its variegated coloration, typically a mottled pink, green, and sometimes clear or gray. It is composed primarily of epidote (green), pink orthoclase feldspar, and colorless quartz. The relative proportions of these minerals can vary, leading to different shades and patterns. It is a relatively hard and durable stone, making it suitable for polishing and carving.

How to Identify

Color: Mottled pink (orthoclase), green (epidote), and often colorless/gray (quartz). The green can range from yellowish-green to dark olive green, and the pink from salmon to reddish-pink.
Luster: Vitreous to sub-vitreous for quartz and feldspar, resinous to vitreous for epidote.
Texture: Granitic to granular, often with interlocking crystals visible to the naked eye. Can be medium to coarse-grained.
Crystal Form: Individual mineral components (quartz, orthoclase, epidote) exhibit their characteristic crystal forms within the rock matrix, though often anhedral due to interlocking growth.
Cleavage: Orthoclase exhibits two distinct cleavages at nearly 90 degrees. Epidote has one perfect cleavage. Quartz has no cleavage but exhibits conchoidal fracture.
Geological Environment: Found in areas where granitic rocks have undergone regional or contact metamorphism and hydrothermal alteration, particularly in orogenic belts and ancient continental shields.

Key Facts

Hardness: 6-7 on Mohs scale (due to quartz and feldspar components)
Specific Gravity: 2.85-3.20 (varies with mineral proportions, epidote is denser)
Crystal System: Monoclinic (epidote, orthoclase), Trigonal (quartz)
Color: Mottled pink, green, and colorless/gray
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), none in quartz
Composition: A granitoid rock composed primarily of epidote (Ca2(Al,Fe)3(SiO4)3(OH)), orthoclase feldspar (KAlSi3O8), and quartz (SiO2).

Quick Check

Color: Mottled pink and green
Luster: Vitreous to sub-vitreous
Streak: White

Physical Characteristics

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

Formation

Unakite is a granitoid rock that has undergone epidotization, a form of hydrothermal alteration. It forms when plagioclase feldspar in granite is replaced by epidote, while the orthoclase feldspar remains largely unaltered, and quartz is also present. This alteration typically occurs under greenschist facies metamorphic conditions, often associated with regional metamorphism or hydrothermal activity along fault zones or intrusive contacts.

Usage

Primarily used as an ornamental stone, for lapidary purposes (cabochons, beads, carvings), and in decorative architectural applications. It is also popular in metaphysical and New Age practices.

Age Distribution

Typically associated with Precambrian to Paleozoic granitic intrusions that have undergone hydrothermal alteration.

Where to Find

Unaka Mountains, North Carolina, USA

The type locality for Unakite, where it was first discovered and named. Found in the Appalachian Mountains.

Virginia, USA

Significant deposits are found in the Blue Ridge Mountains of Virginia, often as river-worn boulders.

South Africa

Occurrences reported in various regions.

Brazil

Known for some deposits, often associated with pegmatitic intrusions.

China

Reported occurrences in several provinces.

Sierra Leone

Deposits have been identified.

Finding Tips

Look in Riverbeds and Glacial Till

Unakite is often found as rounded pebbles and boulders in riverbeds and glacial deposits, as it is relatively resistant to weathering and erosion.

Identify Associated Geology

Search in regions known for granitic intrusions and metamorphic activity, particularly where hydrothermal alteration has occurred.

Recognize the Color Pattern

The distinctive mottled pink and green coloration is the primary visual identifier. Look for areas with these contrasting colors.

Check for Hardness

Unakite is relatively hard (6-7 on Mohs scale), so it will scratch glass and will not be easily scratched by a knife.

Similar Rocks

Epidosite

Also known as: Epidote-rich rock

Granite

Also known as: Granitic rock

Fuchsite Quartzite

Also known as: Green Quartzite

Scientific Classification

Mineral Class: Silicate (epidote, feldspar, quartz)
Group: Metamorphic Rock (specifically, an altered granite)
Crystal System: Monoclinic (epidote, orthoclase), Trigonal (quartz)
Chemical Formula: Variable, as it is a rock composed of multiple minerals: (Ca2(Al,Fe)3(SiO4)3(OH)) + (KAlSi3O8) + (SiO2)
Composition: Epidote, Orthoclase Feldspar, Quartz

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