Epidote shows shades of green, yellow, gray, grayish white, greenish black, black; usually very dark. Clinozoisite is colorless, pale yellow, gray, green, pink; often zoned. Piedmontite is reddish brown, black, rose red, pink. Allanite is light brown to black. Hancockite is brownish or black.
Most members of the group have non-diagnostic spectra. Epidote has a very strong line at 455 nm. Sometimes, a weak line is seen at 475 nm. This spectrum is very sensitive to direction within the material and isn't visible in certain orientations.
Epidote is derived from the Greek for “increase,” since the base of the prism has one side longer than the other. Clinozoisite is the monoclinic dimorph of zoisite. Piedmontite (or piemontite) is named after the locality in Italy, Piemonte (Piedmont). Unakite is named after the Unaka range of mountains in the United States. Allanite is named after mineralogist T. Allan. Tawmawite is named after the Myanmar locality. Mukhinite is named after A. S. Mukhin, Soviet geologist.
The minerals of the epidote group form at low temperatures in low to medium-grade metamorphic rocks. Allanite is more commonly found in igneous rocks such as pegmatites. Clinozoisite and epidote are also found in igneous rocks, and piedmontite is found in schists and manganese ore deposits.
Nevertheless, the supergroup still includes some interesting gemstones, both common and rare. It features species suitable for faceting and cabbing as well as beautiful crystals for collecting. These materials often contain fibrous inclusions. On rare occasions, they create a chatoyant “cat’s eye” effect in cabbed epidotes and clinozoisites.
Usually so dark in color, large faceted epidotes result in nearly black, lifeless gems. However, small stones, under 3 to 4 carats, can often turn out as bright and lively faceted gems.
Pistazite or pistacite is a trade name for yellowish green “pistachio-colored” epidote.
These gems would actually make better looking faceted pieces than epidotes. Although clinozoisites aren’t rare, they occur rarely in sizes over 5 carats. Other localities occasionally yield fine gems. Clinozoisite rarely occurs in pure form. It usually contains some iron, like its series brother, epidote. Clinozoisite shares a chemical formula and outward appearance (but not a crystal system) with zoisite.
Very dark in color and seldom cut, allanite contains rare-earth and radioactive elements. As a result, these gems become metamict. In other words, they have severe damage to their internal crystalline structure.
This New Jersey gemstone is very rare. Faceted pieces, if any exist, would weigh under 1 to 2 carats.
This very rare mineral occurs in small grains. First discovered in Gornaya Shoriya, Russia, no cut specimens exist.
Also known as piemontite, this species is sometimes confused with thulite, a pink manganiferous variety of zoisite. While thulite sometimes appears bright pink, piedmontite typically has a dark brown or reddish color. Thulite can occur in large pieces, but piedmontite seldom occurs in large masses. However, both materials can make lovely cabochons.
A very rare, deep emerald-green colored variety of epidote from Myanmar, this material gets its color from chromium.
A popular material for cabochons, unakite, an altered granite, contains green epidote, white to gray quartz, and pink feldspar (orthoclase). The United States produces and exports this widely used lapidary rock, but Ireland, Zimbabwe, and other countries also produce similar material.
Blue Ridge, Unaka Range, North Carolina produces this lapidary material. Other sources include Virginia and Georgia. In addition, Zimbabwe yields a similar rock.
Unakite occurs in huge blocks weighing many pounds. Gem cutters often cut it into spheres as well as cabs. Facetable epidote is rare over 5 carat sizes. Cut clinozoisite tends to be even smaller. Allanite is rarely ever cut, except as cabochons. Piedmontite is opaque and massive. It’s also cut only as cabochons.
Some epidotes may have a hardness of 7, on par with quartz. However, most gem materials in this supergroup have a hardness of 6 or softer. Since these gems also have perfect cleavage and sensitivities to heat and acids, clean them only with a soft brush, mild detergent, and warm water. For jewelry use, have these stones set in protective settings and/or reserve them for occasional wear. For more recommendations, consult our gemstone jewelry care guide.