File:Unakite (epidotic granite).jpg

English: Unakite is a distinctive rock consisting of greenish epidote (Ca2(Al,Fe)3(SiO4)3(OH)), salmon-colored potassium feldspar (KAlSi3O8), and gray quartz (SiO2). This rock is granite that has been metasomatized, which refers to metamorphism by chemical alteration. In this case, the original plagioclase feldspar and/or mafic mineral content of the granite has been altered to epidote. Epidote is a low-temperature metamorphic mineral. It usually forms along fractures or faults in granite. Hydrothermal fluids (hot water) in the fractures will alter the adjacent country rocks by selectively changing the plagioclase and mafic minerals.

Epidote-rich rocks can form by regional metamorphism of shale. From low to higher grade metamorphism, many shales will alter to chlorite schist to epidote-rich rocks to actinolite-rich rocks. These are the greenschists.

Epidote can also occur in pegmatites, which are very coarsely-crystalline, intrusive igneous rocks. Incompatible and rare elements get concentrated near the end of pegmatite crystallization - epidote is a "garbage can" mineral that often forms in such settings. If the epidote ends up having thorium, which is radioactive, surrounding quartz will usually be altered to smoky quartz.

Tumble-polished unakite is considered a semiprecious stone.

Locality: unrecorded/undisclosed site, but probably from the Appalachian Mountains of eastern USA