Epidote Value, Price, and Jewelry Information


EPIDOTE: Baja California, Mexico (1.0), Kenya (1.2). Photo © Joel E. Arem, PhD, FGA. Used with permission.

The epidote group consists of three related minerals that are fairly well known to collectors and hobbyists, plus one popular gem mineral and three less common species.

Epidote Value

Highest values go to transparency, color, and size.

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Epidote Value via Gem Price Guide

Epidote Information

DataValue
NameEpidote
Crystallography All are monoclinic, except Zoisite which is orthorhombic. Crystals prismatic and tabular; also granular, massive, fibrous; sometimes twinned, often striated.
Colors Epidote GRN YEL GRY BLK Usually very dark. Zoisite GRY GRN BRN PINK YEL BLU VIO. Clinozoisite COLORLESS YEL GRY GRN PINK. Piedmontite BRN BLK RED PINK. Allanite BRN BLK. Hancockite BRN BLK.
Luster Vitreous; pearly on cleavages; massive materials dull. Allanite resinous, pitchy.
Polish Luster Vitreous to greasy, allanite resinous
Fracture Luster Vitreous, pearly, dull
Fracture Conchoidal to uneven; brittle.
Hardness 6-7. Epidote sometimes slightly harder, piedmontite softer.
Toughness Fair to poor
Specific Gravity See table below.
Cleavage Perfect 1 direction in all (different orientation in zoisite).
Dispersion For tanzanite: 0.019. Values for other epidote group minerals are in the same range.
Stone SizesTanzanite, faceted to large. Other species faceted, usually under 5 carats. All species, cabochons to very large.
Heat SensitivityYes
Luminescence Usually none. Thulite (pink zoisite) from Nevada sometimes medium pale brown in SW. Also thulite from North Carolina is orangy-yellow in LW.
Enhancements Tanzanite, heat treatment, common. Others species, none known.
Transparency Transparent to Opaque
UV LongUsually inert, not diagnostic
UV ShortUsually inert, not diagnostic
Absorption Spectrum Epidote, directional, strong line at 455 nm, weak line at 475 nm. Tanzanite, broad absorption centered at 595 nm, weak lines at 528 and 455 nm. Others not diagnostic.
Identifying Characteristics Tanzanite, strong pleochroism.

Comments

The epidote minerals are very interesting and span a wide range of the gem market. The epidote group consists of three related minerals that are fairly well known to collectors and hobbyists, plus one popular gem mineral and three less common species.

Hancockite, from New Jersey is very rare, and if a faceted gem exists it would be extremely small (under 1-2 carats).

Epidote is usually so dark in color that a large faceted gem is nearly black. lifeless, and uninteresting; small stones, under 3-4 carats, are often bright and lively, however.

Clinozoisite would be a better-looking gem, but is very rare in sizes over 5 carats. The only well-known gem source is Baja, Mexico, though an occasional crystal from another locality yields a fine gem.

Allanite is very dark in color and seldom cut. The content of rare earth and radioactive elements causes it to become metamict with severe damage to the internal crystalline structure.

Unakite is a widely used and popular cabochon material that is exported throughout the world. It is best known from the United States, but Ireland, Zimbabwe, and probably other countries have similar rocks.

Mukhinite is a very rare mineral, in small grains from Gornaya Shoriya, USSR, and has never been cut.

Piedmontite is a distinct species but is often confused with thulite, which is a pink manganiferous variety of the species zoisite; piedmontite is dark brown or reddish in color, seldom in large masses, whereas thulite can occur in large pieces and is often bright pink in color. Both materials make lovely cabochons.

Pure clinozoisite is very rare; it usually contains some iron, and there is a complete solid-solution series from it to epidote.

Tawmawite is a deep emerald-green epidote from Burma, the color of which is due to chromium. This material is very rare.

Tanzanite is the best known member of the epidote group and is a variety of zoisite. The name was given by Tiffany & Co. in connection with a trade promotion, and has stuck although it has no mineralogical significance. Tanzanite occurs in a variety of colors at the Tanzanian locality, but most crystals are heated to about 700°F to create a deep, intense blue with violet dichroism. Tanzanite is soft and brittle, considering it is a popular ringstone, and great care should be exercised in wearing it. Inclusions that have been noted in tanzanite include actinolite, graphite, and staurolite.

Epidote group materials often contain fibrous inclusions that create a chatoyancy and yield catseye gems when cut into cabochons. Catseye clinozoisite and epidote are known. Catseye tanzanites are very rare but have been found.

Formula

The general formula of the epidote group is X2Y3Z3(O,OH,F)13 where X= Ca, Ce, La, Y, Th, Fe, Mn; Y=Al, Fe, Mn, Ti; Z=Si, Be.

  • Zoisite and Clinozoisite:Ca2Al3Si3O12(OH)
  • Epidote: Ca2(AlFe)3SiO12(OH)
  • Piedmontite: Ca2(Mn, Fe ,AI )3Si3O12(OH) (also called piemontite).
  • Allanite: (Ca, Ce, La,Y)2(Mn, Fe, Al)3Si3O12(OH)
  • Mukhinite: Ca2(Al2V)Si3O12(OH). Hancockite: (Pb, Ca, Sr)2(Al, Fe) 3Si3O12(OH).
ZOISITE: Thulite, Norway (each specimen ~2 inches across)
ZOISITE: Thulite, Norway (each specimen ~2 inches across). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Colors

  • Clinozoisite is colorless, pale yellow, gray, green, pink; often zoned.
  • Epidote shows shades of green, yellow, gray, grayish white, greenish black, black.
  • Piedmontite is reddish brown, black, rose red, pink.
  • Hancockite is brownish or black.
  • Allanite is light brown to black.
  • Zoisite is gray, green, brown, pink (thulite), yellowish, blue to violet (tanzanite).

Pleochroism

  • None in clinozoisite. Distinct red to yellowish brown in hancockite.
  • Allanite: reddish brown/brownish yellow/greenish brown; light brown/brown/dark red-brown; colorless/pale green/green.
  • Epidote: colorless, pale yellow or yellow-green/greenish yellow/yellow-green.
  • Zoisite: deep blue/purple/green (tanzanite); reddish purple/blue/yellowish brown (tanzanite): pale pink/ colorless/yellow; dark pink/pink/yellow (thulite).
  • Piedmontite: yellow/amethyst ine violet/red.

Spectral

Most members of the group have nondiagnostic spectrum; epidote has a very strong line at 4550, weak line is sometimes seen at 4750. This spectrum is very sensitive to direction within the material and is not visible in certain orientations. Tanzanite has a broad absorption in the yellow-green centered at 5950, with faint bands also at 5280 and 4550 and a few weak lines in the red.

Occurrence

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. Zoisite occurs in calcareous rocks such as metamorphosed dolomites and calcareous shales subjected to regional metamorphism.

Epidote:

  • McFall Mine, Ramona, California; Idaho; Colorado; Michigan; Connecticut; Massachusetts; New Hampshire. Baja California, Mexico; Arendal, Norway; Czechoslovakia; USSR; Japan; Korea: Australia; Kenya; Madagascar.
  • Switzerland: many localities.
  • Bourg d’Oisans, France: fine crystals.
  • Italy: Piedmont, other localities.
  • Untersulzbachthal, Austria: main source of faceting rough.
  • Burma: at Tawmaw, a chrome-rich material, fine deep green color (tawmawite).
  • Sri Lanka: yellow-brown (pleochroism = yellow-green/ brown/greenish-yellow); a= 1.718;  β= 1.734; γ= 1.738; birefringence = 0.020; S.G. = 3.33.
  • Outokumpu, Finland: chromiferous epidote (tawmawite).
  • Minas Gerais, Brazil: cuttable, yellowish-green crystals (these are trichroic, low in iron; indices 1.722/1.737/1.743; birefringence 0.021; density 3.3-3.5).
  • Blue Ridge, Unaka Range, North Carolina (also in Virginia, Georgia): unakite, a granite consisting of pink feldspar and green epidote. A similar rock is also known from Zimbabwe.

Clinozoisite:

CLINOZOISITE: Mexico (1.18)
CLINOZOISITE: Mexico (1.18). Photo © Joel E. Arem, PhD, FGA. Used with permission.
  • Nevada; Colorado.
  • Timmons, Ontario, Canada; Ireland; Iceland; India; Raly; Switzerland; Austria; Czechoslovakia.
  • Kenya: gray-green crystals.
  • Gavilanes, Baja, Mexico: brownish facetable crystals.

Piedmontite:

PIEDMONTITE: Adams County, Pennsylvania (~4 inches across)
PIEDMONTITE: Adams County, Pennsylvania (~4 inches across). Photo © Joel E. Arem, PhD, FGA. Used with permission.
  • Pennsylvania; Missouri
  • Scotland; Vermland, Sweden; Morbihan, France; Japan; Otago, New Zealand California and Arizona: many localities.
  • Piemonte, Italy: in sericite schists.
  • Egypt: in a porphyry, colored red by piedmontite.

Hancockite:

  • Franklin, New Jersey: only notable locality, in small crystals.

Allanite:

  • Various localities throughout the United States.
  • Canada; Norway; Sweden; Greenland; USSR; Madagascar

Zoisite:

  • South Dakota; Massachusetts.
  • Wyoming: greenish-gray material, sometimes tumble polished for jewelry. Washington: thulite.
  • California and Nevada: thulite.
  • North Carolina: thulite.
  • Baja, Mexico; Scotland; Austria; Finland; USSR; Japan; Germany.
  • Longido, Tanzania: deep green crystals, colored by chromium, with ruby crystals.
  • Lelatema, Tanzania: fine blue-violet crystals, up to large size, often gemmy (tanzanite).
  • Norway: thulite.
  • Greenland: thulite.
ZOISITE: Tanzanite. Tanzania, unheated, showing natural color range (~ 0.5 to 5)
ZOISITE: Tanzanite. Tanzania, unheated, showing natural color range (~ 0.5 to 5). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Stone Sizes

Unakite occurs in huge blocks weighing many pounds and is often cut into spheres as well as cabochons. Facetable epidote is rare over 5 carat sizes, and cut Clinozoisite tends to be even smaller. Allanite is hardly ever cut except as cabochons: piedmontite is opaque and massive, also cut only as cabochons. Tanzanite is the only member of the epidote group that reaches large sizes in faceted gems. Rough tanzanite crystals weighing hundreds of carats have been found.

  • Smithsonian Institution (Washington, D.C): 122.7 (blue, tanzanite, Tanzania); 18.2 (blue catseye tanzanite, Tanzania); 3.9 (epidote, brown, Austria).
  • Devonian Group (Calgary, Alberta, Canada): 7.30 (clinozoisite, brownish, Iran); 6.90 (epidote, brown).
  • Private Collection: 220 (blue, tanzanite, Tanzania); 15 (clinozoisite, light brown-green, Baja).

Clinozoisite

Epidote

Piedmontite

Hancockite

Allanite

Tanzanite

Zoisite

Thutile

Density

3.21-3.38

3.38-3.49

3.45-3.52

4.03

3.4-4.2

3.35

3.15-3.38

3.09

Optics

a

1.670-1.715

1.715-1.751

1.732-1.794

1.788

1.640-1.791

1.692

1.685-1.705

1.695

β

1.675-1.725

1.725-1.784

1.750-1.807

1.810

1.650-1.815

1.693

1.688-1.710

γ

1.690-1.734

1.734-1.797

1.762-1.829

1.830

1.660-1.828

1.700

1.697-1.725

1.701

2V

(+)14-90°

(-)90-116°

(+)2-9°

(-)50°

(+-) 40 -123°

(+)

(+)0-60°

(-)

Birefringence

0.005-0.015

0.015-0.049

0.025-0.073

0.042

0.013-0.036

0.009

0.004-0.008

0.006

 

ZOISITE: Tanzanite, Tanzania (26.54)
ZOISITE: Tanzanite, Tanzania (26.54). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Name

Epidote is derived from Greek for increase because the base of the prism has one side longer than the other. Zoisite is named after Baron von Zois, who presented Werner, the great mineralogist, with the first specimens of the material. Thulite is after Thule, the ancient name for Norway. Tanzanite is the Tiffany & Co. trade name for blue zoisite, named after the country of origin, Tanzania. Clinozoisite is the monoclinic dimorph of zoisite. Piedmontite (piemontite) is 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 Burmese locality. Mukhinite for A. S. Mukhin, Soviet geologist.

Variety Names

Zoisite:

  • Tanzanite, transparent blue and violet
  • Thulite, translucent to opaque pink. National gem of Norway.

Trade Names

  • Unakite, green epidote with white to gray quartz, and pink feldspar
  • Pistacite, yellowish green epidote
  • Ruby in zoisite, ruby crystals in massive, green zoisite.
  • Rosaline, thulite.
  • Unionite, thulite.