| Metamorphic rock | |
 Tumble polished unakite pebbles | |
| Composition | |
|---|---|
| Orthoclase feldspar,epidote,quartz | |
| Physical Characteristics | |
| Fabric | Mottled |
| Relationships | |
| Protoliths | Granitoids andcharnockite |
Unakite is a coarse-grainedmetamorphic rock that is an alteredgranitoid composed oforthoclase feldspar (pink),epidote (yellow-green), andquartz (smokey or colorless).Albite-oligoclaseplagioclase (white) may or may not be also present.[1][2]
Bradley first defined and described Unakite in 1874. He named it forUnaka Range of theGreat Smoky Mountains of westernNorth Carolina and EasternTennessee. He collected his samples primarily from "The Bluff", "Walnut Mountain", and "Max's Patch" inCocke County, Tennessee.[3]
Generally, unakite is interpreted to be ametamorphic rock created by thehydrothermal alteration of eithergranite,granodiorite, orcharnockite. It is argued that the epidote in unakite was created by the alteration of eithermafic minerals;[3]biotite and feldspar;[4][5] or some combination of these minerals by hydrothermal fluids. It is also possible that some of the epidote is the result of directprecipitation from hydrothermal fluids.[6][7]
Most commonly, unakite occurs as comparatively small and restricted bodies in granite and granodiorite. Typically, these bodies are not larger than 15 m (49 ft) in any dimension. In these granitoids, unakite also occurs asveins,dike-like bodies, lenses, irregular masses, or combinations of these.[6][7]
Locally inShenandoah National Park, hydrothermal alteration has convertedcharnockites of theCatoctin Formation to unakite, characterized by green epidote, pink feldspar and blue quartz.[8][9] Where thelava flows of theNeoproterozoic Catoctin Formation directly overlie it, the dark-greenish-gray charnockite is typically bleached light gray due to therecrystallization of its plagioclase and alkali feldspar. Alongjoints, the migration of hydrothermal fluid induced by heat from the overlying lava has altered the charnockites to unakite. Overall, unakite in Blue Ridge region is associated with either Neoproterozoic extrusion of lavas of the overlying Catoctin Formation; enhanced fluid flow associated withfault zones; or local effects of regionalPaleozoicmetamorphism.[10]
The distribution of unakite is not precisely known. In part, this lack of knowledge it is due to inconsistencies in how unakite is defined and inconsistent classification of it under other names. It occurs in at least 30 locations in the United States including a few places west of the Mississippi River.[6][7] Still, the majority of finest unakite is largely restricted to the Blue Ridge region of North Carolina and Virginia with lessor quality unakite found in westernmost Tennessee.[11]
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Although found exposed in roadcuts, crush stone pits, and other excavation in the Blue Ridge region, high quality unakite is also found in the stream beds as rolled, well-rounded stones as in the Rose River, northwest ofSyria, inMadison County, Virginia. The stones have a rusty surface experience and vary in size from cobbles to boulders.[12][13]
When collecting in the Blue Ridge region, it must be remembered that unakite occurs in national and state parks in which, of course, rock collecting is prohibited by law. Rock hunting is permitted in national forests, except in certain designated areas. Outside of the parks, the state and national forests, the land is all privately owned, and land owner permission is required for collecting, even if the land is rugged and mountainous and seemingly deserted.[11][13]
Elsewhere in the United States, the occurrence of unakite has been reported. Within the eastern United States, unakite has been reported from Passic County, New Jersey[6] andMarblehead Neck, Massachusetts.[14] In the Midwest, unakite of unknown quality has also been reported from the Waupacaadamellite fromWaupaca County, Wisconsin.[15] Finally, in the western United States, unakite has also been reported fromTeller County, Colorado andBernalillo County, New Mexico.[6]
Unakite has also been reported and listed as having been found at locations outside of North America. For example, Wahl reports the occurrence of unakite within northeasternFinland at about 30 to 40 locations. These unakites are often associated withhypersthene granites.[16] Unakite is listed by Manutchehr-Danai, without any accompanying documentation, as having been found inZimbabwe,Ireland, andSouth Africa.[17]
A good quality unakite is considered asemiprecious stone; it will take a good polish and is often used injewelry as beads orcabochons and otherlapidary work such as eggs, spheres and animal carvings.[6][12][13]
