metamorphic
Unakite (or Epidotized Granite)
Epidotized Granite (Composition: KAlSi3O8, Ca2(Al,Fe)3(SiO4)3(OH), SiO2)
Hardness: 6-7 (Mohs scale); Color: Mottled green (epidote), pink (orthoclase feldspar), and gray (quartz); Luster: Vitreous to dull; Crystal structure: Monoclinic/Triclinic (as a rock, it is an aggregate); Cleavage: Poor/Irregular fracture; Specific Gravity: 2.85–3.20
- Hardness
- 6-7 (Mohs scale)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Mottled green (epidote), pink (orthoclase feldspar), and gray (quartz); Luster: Vitreous to dull; Crystal structure: Monoclinic/Triclinic (as a rock, it is an aggregate); Cleavage: Poor/Irregular fracture; Specific Gravity: 2.85–3.20
Formation & geological history
Formed through hydrothermal metamorphism where granite is altered by hydrothermal fluids. Plagioclase feldspar is replaced by green epidote while orthoclase remains. Most common in Precambrian and Paleozoic terranes.
Uses & applications
Used primarily as a decorative stone, in lapidary work for cabochons, beads, and carvings. Also used as architectural stone for floor tiles or facing stone.
Geological facts
First discovered in the Unaka Range of North Carolina, USA, from which it derives its name. It is unique because it is a rock that is frequently treated as a semi-precious gemstone due to its striking color contrast.
Field identification & locations
Identify in the field by its distinct 'pistachio' green and 'salmon' pink mottled appearance. Commonly found in river beds and glacial till in the Blue Ridge Mountains and Lake Superior regions. It will not react to acid and is hard enough to scratch glass.
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