Unakite

Metasomatized Granitoid (Altered Granite)

Unakite (a type of altered granite composed of epidote, pink orthoclase feldspar, and quartz)

Also known as: Epidotized Granite, Epidote-Feldspar-Quartz Rock

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Description

Unakite is a distinctive altered granitic rock characterized by its variegated appearance, typically displaying shades of pistache green, salmon pink, and often colorless to greyish-white. It is composed primarily of epidote (green), pink orthoclase feldspar, and colorless to greyish quartz. The proportions of these minerals can vary, leading to different patterns and color intensities. It is not a true mineral but a rock, specifically a metasomatized granite.

How to Identify

Color: Distinctive mottled or speckled pattern of pistache green (epidote), salmon pink (orthoclase feldspar), and colorless to greyish-white (quartz).
Luster: Vitreous to sub-vitreous for quartz and feldspar, resinous to vitreous for epidote.
Texture: Granitic to granoblastic, medium to coarse-grained, interlocking crystalline texture.
Crystal Form: Individual mineral components (epidote, orthoclase, quartz) may show anhedral to subhedral forms within the rock matrix.
Cleavage: Orthoclase exhibits two distinct cleavages at nearly 90 degrees. Epidote has one perfect cleavage. Quartz has no cleavage.
Geological Environment: Found in areas where granitic rocks have undergone regional or contact metamorphism and hydrothermal alteration, particularly in orogenic belts.

Key Facts

Hardness: 6-7 (Mohs scale, due to constituent minerals)
Specific Gravity: 2.85 - 3.20 (variable, depending on mineral proportions, epidote is denser)
Crystal System: Monoclinic (epidote, orthoclase), Trigonal (quartz) - as a rock, it's an aggregate of these systems.
Color: Green (epidote), pink (orthoclase), colorless/grey (quartz)
Luster: Vitreous to sub-vitreous
Transparency: Opaque to translucent
Fracture: Uneven to conchoidal (quartz), irregular (feldspar, epidote)
Cleavage: Good in orthoclase (two directions at ~90°), perfect in epidote (one direction), absent in quartz.
Composition: An aggregate of epidote (Ca2(Al,Fe)3(SiO4)3(OH)), orthoclase feldspar (KAlSi3O8), and quartz (SiO2).

Quick Check

Color: Mottled green, pink, and white/grey
Luster: Vitreous to sub-vitreous
Streak: White

Physical Characteristics

Crystal Habit: Granular to massive aggregate of anhedral to subhedral crystals.
Cleavage Type: Good in orthoclase, perfect in epidote, none in quartz.
Fracture Type: Uneven to conchoidal.
Tenacity: Brittle.
Luster Type: Vitreous to sub-vitreous.

Formation

Unakite forms from the metasomatic alteration of granitic rocks. This process involves the replacement of plagioclase feldspar (specifically calcium-rich varieties) by epidote, often facilitated by hydrothermal fluids rich in calcium, aluminum, iron, and silica. The potassium feldspar (orthoclase or microcline) and quartz components of the original granite are generally more resistant to this alteration and remain, contributing to the characteristic pink and colorless components, respectively. The green epidote forms from the breakdown of plagioclase and mafic minerals (if present) in the original granite.

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 orogenic events, often Precambrian to Paleozoic, but can form whenever granitic rocks undergo appropriate hydrothermal alteration.

Where to Find

Unaka Mountains, North Carolina, USA

The type locality where Unakite was first discovered and named. It is found in the Appalachian Mountains.

Virginia, USA

Significant deposits are found in the Blue Ridge Mountains of Virginia, often as pebbles and boulders in stream beds.

Brazil

Known for producing large quantities of Unakite, often with vibrant colors.

South Africa

Deposits are found in various regions.

China

Sources of Unakite are present in several provinces.

Sierra Leone

Reported occurrences of Unakite.

Scandinavia

Found in parts of Norway and Sweden.

Finding Tips

Look in Stream Beds

Unakite is often found as water-worn pebbles and boulders in alluvial deposits, especially in areas where its parent granitic rocks have eroded.

Identify Granitic Terrains

Focus your search in regions known for granitic intrusions and associated metamorphic or hydrothermal alteration zones.

Recognize Color Pattern

The distinctive green, pink, and white/grey mottled pattern is the primary identifier. Look for these specific color combinations.

Check Hardness

The overall hardness will be around 6-7 on the Mohs scale due to the presence of quartz and feldspar, making it resistant to scratching by a steel knife.

Similar Rocks

Epidosite

Also known as: Epidote Rock

Granite

Also known as: Granitic Rock

Gneiss

Also known as: Banded Metamorphic Rock

Scientific Classification

Mineral Class: Rock (not a single mineral)
Group: Metasomatized Granitoid
Crystal System: Polycrystalline aggregate (constituent minerals are Monoclinic and Trigonal)
Chemical Formula: Variable, composed of Epidote (Ca2(Al,Fe)3(SiO4)3(OH)), Orthoclase (KAlSi3O8), and Quartz (SiO2).
Composition: Silicate minerals (epidote, orthoclase, quartz).

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