Tanzanite (Zoisite) Value, Price, and Jewelry Information

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Medium violet-blue, triangle-cut tanzanite, 1.62 cts, 8 mm, Tanzania. © The Gem Trader. Used with permission.

Tanzanite has had a rapid rise to prominence among jewelers and gem enthusiasts. Although naturally reddish brown, this transparent zoisite variety achieves a stable, beautiful blue to violet color with heat treatments.

Tanzanite (Zoisite) Value

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Faceted - Top Color: vB 6/5

.5 to 1 carat
SI to Clean
to /ct
1 to 3 carats
SI to Clean
to /ct
5 carats plus
SI to Clean
to /ct
Accompanying value information:
View Tanzanite (Zoisite) Profile

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tanzanite - gold Celtic ring

Blending 14k yellow and white gold creates great contrast in this Celtic-inspired design. The yellow gold setting complements the purple-blue tanzanite perfectly. A low-profile bezel setting ensures the tanzanite is well protected and unlikely to snag with daily wear. © CustomMade. Used with permission.

In general, tanzanites showing more blue are valued higher than those showing more violet. Medium dark colors are the ideal. Custom cuts add value. As always, size and clarity have a strong effect on prices. Large clean rough is extremely scare.

Ultra-rare cat’s eye tanzanites are highly prized.

cat's eye tanzanite

Violetish blue cat’s eye tanzanite with a very sharp eye, 0.79 cts, 5 mm, Tanzania. © The Gem Trader. Used with permission.

Among other varieties of zoisites, extremely rare green zoisites are highly sought by collectors. These are sometimes confusingly referred to as “green tanzanite.”

See our tanzanite buying guide for more detailed value information.

unheated green zoisite - Tanzania

Unheated green, oval brilliant-cut zoisite, 0.94 cts, 7.6 x 4.9 mm. Tanzania. © The Gem Trader. Used with permission.

Tanzanite (Zoisite) Information

Data Value
Name Tanzanite (Zoisite)
Is a Variety of Zoisite
Crystallography Orthorhombic
Crystallographic Forms
Refractive Index Zoisite varieties, including tanzanite, have different RIs: 1.685-1.725. See "Identifying Characteristics" below.
Colors Gem-quality zoisites can be gray, green, brown, pink, or yellowish. Color zoning may occur. Thulite can be pink. With heating, tanzanite can be blue to violet.
Luster Vitreous
Hardness 6-7
Wearability Good
Fracture Conchoidal to uneven
Specific Gravity 3.09-3.38. (Tanzanite 3.35). Varies by zoisite variety, see "Identifying Characteristics" below.
Birefringence Zoisite varieties, including tanzanite, have different birefringence values: 0.004-0.009. See "Identifying Characteristics" below.
Cleavage Perfect
Dispersion 0.019 (tanzanite)
Heat Sensitivity Yes
Luminescence Thulite (pink zoisite) from Nevada is sometimes medium pale brown in SW. Also thulite from North Carolina is orangey-yellow in LW.
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Long, UV-Short
Enhancements Virtually all tanzanite is heat treated. Coatings to improve color and luster, some coatings add iridescence.
Typical Treatments Heat Treatment, Surface Coating
Special Care Instructions Avoid rough treatment
Transparency Tanzanite is transparent. Other gem-quality zoisites may be transparent to opaque.
Absorption Spectrum Tanzanite: broad absorption in the yellow-green centered at 595 nm, weak bands at 528 and 455 nm, and a few weak lines in the red.
Phenomena Chatoyancy (rare, tanzanite). Surface coated/enhanced tanzanites may show iridescence, but this is not a natural property. Color change.
Birthstone December
Formula Ca2Al3(SiO4)3(OH)
Pleochroism Very strong. See "Identifying Characteristics" below.
Optics Zoisites, including tanzanite, are Biaxial (+). However, thulite is Biaxial (-). Zoisite varieties have varying optic properties. See "Identifying Characteristics" below.
Optic Sign Biaxial +, Biaxial -
Etymology Zoisite is named after Baron Sigmund Zois, who presented the first specimens of the material to Abraham Gottlob Werner, the great mineralogist. Thulite is named after Thule, an ancient name for Norway. Anyolite comes from the Masai anyoli for “green.” Tanzanite is the Tiffany & Co. trade name for blue zoisite, named after the country of origin, Tanzania.
Occurrence Zoisite occurs in calcareous rocks such as metamorphosed dolomites and calcareous shales subjected to regional metamorphism.
Inclusions Zoisite may contain fingerprints, healed cracks, and growth tubes. Minerals found included in tanzanite include actinolite, graphite, and staurolite.

Tanzanite (10.18). Photo © Joel E. Arem, PhD, FGA. Used with permission.

What Color is Tanzanite?

Before the discovery of tanzanite, the known varieties of zoisite made little impact on the gem market. Discovered in the shadow of Mt. Kilimanjaro in 1967, tanzanites show both dramatic color change and pleochroism. In natural light, tanzanites can appear an almost sapphire blue. In fluorescent light, they may appear more violet or amethyst-like. Naturally trichroic, these gems can show blue, red-violet, and yellow-green colors when viewed through each of its three crystal axes.

Their most coveted property, however, is their blue to violet color. Although Mother Nature very rarely produces a blue to violet stone in the rough (via the slow heat of the Sun), almost all tanzanites must receive artificial heat treatments to achieve that prized color. Typically, they’re heated to about 500-600º C or 932-1,112º F.

7 carat Blue-Violet Tanzanite, re-polished by Daniel Stair

Blue-violet tanzanite, 7 cts, re-polished by Daniel Stair. © Dan Stair Custom Gemstones. Used with permission.

What is “Fancy Color Tanzanite?”

Tanzanites are the most well-known members of the zoisite gem species. Not surprisingly, some vendors will try to associate zoisites of other colors with the tanzanite name. You may encounter green, yellow, and pink zoisites sold as “fancy color tanzanites.” Even though these are rare, beautiful colors, the tanzanite name has more caché with the general public and may command higher prices.

By definition, tanzanites are blue to violet zoisites, whether they receive heat treatment or not. Non-blue zoisites should simply be called zoisites.

zoisites

Zoisites in various colors (5.5, 9.9, 2.72, 9.5, 2.05). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Other Zoisite Gem Varieties

Tanzanites will certainly appeal to those interested in truly modern gemstones. Jewelers have even designated this gem a modern option for the December birthstone. However, other gem-quality varieties of zoisite deserve mention, too.

Zoisite

Transparent, gem-quality zoisites occur in many colors and can make beautiful gemstones.

tanzanite - yellow zoisite

Faceted, “wine yellow” zoisite, 1.44 cts, Tanzania. Photo by DonGuennie. Licensed under CC By-SA 4.0.

Thulite

The national gemstone of Norway, this pink, translucent to opaque material can make beautiful cabochons. Faceted pieces are rare. Trade names for thulite include unionite and rosaline.

thulite earrings

Thulite earrings, Kitimat, British Columbia, Canada. Photo by pensondesignergems. Licensed under CC By 2.0.

Anyolite (Ruby-in-Zoisite)

This lapidary rock contains chrome-rich green zoisite, black hornblende, and large, but opaque, ruby. Gem cutters can make cabochons and carvings from this material. This material is also known as ruby-in-zoisite.

anyolite

Carved anyolite ball, 120 mm, Tanzania. Photo by Adam Ognisty. Licensed under CC By-SA 2.0.

Identifying Characteristics

Optics and Specific Gravity

Tanzanite Zoisite Thulite
Specific Gravity 3.35 3.15-3.38 3.09
Optics
a 1.692 1.685-1.705 1.695
β 1.693 1.688-1.710
γ 1.7 1.697-1.725 1.701
2V (+) (+) 0-60° (-)
Birefringence 0.009 0.004-0.008 0.006

Pleochroism

Tanzanite

  • Violet color: reddish purple/blue/yellowish brown.
  • Blue color: blue/red-violet/yellow-green.

Thulite

  • Pale pink/colorless/yellow.
  • Dark pink/pink/yellow.

Above, this strongly trichroic tanzanite crystal shows blue, purple, and red/maroon along different axes. Crystal 3.3 x 3.1 x 1.5 cm, Merelani Mines, Tanzania. © Rob Lavinsky, www.iRocks.com. Used with permission.

Is There Lab-Created Tanzanite?

To date, synthetic tanzanites are unknown. However, many simulants (imitations) do exist. Consult our buying guide for more information.

Is All Tanzanite Enhanced?

Assume all blue to violet tanzanites have received heat treatment. This is a stable treatment.

unheated, faceted tanzanites (zoisites)

Unheated tanzanites, showing natural color range (~ 0.5 to 5). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Zoisite Sources

Tanzanite

The sole source of tanzanite is the Merelani Hills in the Lelatema Mountains, Tanzania. The mines here produce fine blue to violet crystals, up to large size, and often gemmy.

tanzanite

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

There are four “blocks” of tanzanite-producing mines in Tanzania. However, despite claims that “D-Block” tanzanites have superior quality, there’s no difference in tanzanite quality between these mines and no way to distinguish materials from specific mines.

Anyolite

Longido, Tanzania produces deep green crystals, colored by chromium, with ruby crystals.

Thulite

  • United States: California; Nevada; North Carolina; Washington.
  • Canada; Greenland; Japan; Norway.
thulite - Norway

Thulites, Norway (each specimen about 2 inches across). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Gem-Quality Zoisite

Other sources of gem-quality zoisites include the following:

  • United States: Massachusetts; South Dakota; Wyoming (greenish-gray material, sometimes tumble polished for jewelry).
  • Austria; Finland; Germany; Baja California, Mexico; Pakistan; Russia; Scotland.
green zoisite - Pakistan

Gray-green, rectangular cushion-cut zoisite, 2.34 cts, 8.7 x 7 mm, Pakistan. © The Gem Trader. Used with permission.

How Large Can Tanzanites Get?

Tanzanites, alone of all zoisite varieties, can reach large sizes in faceted gems. Rough crystals weighing hundreds of carats have been found.

  • Smithsonian Institution (Washington, DC): 122.7 (blue, tanzanite, Tanzania); 18.2 (blue cat’s eye tanzanite, Tanzania).
  • Private Collection: 220 (blue, tanzanite, Tanzania).

Caring for Your Tanzanite Jewelry

For faceting and gem design recommendations for tanzanites and other zoisite varieties, consult this article.

Although tanzanite hardness may range from 6 to 7, its tendency to cleave and brittleness pose hazards for daily wear. Reserve these gems for occasional pieces or use protective settings. Clean them only with a soft brush, mild detergent, and warm water. For more recommendations, consult our gemstone jewelry care guide.

tanzanite and diamond jewelry

Tanzanite and diamond jewelry. Photo © Joel E. Arem, PhD, FGA. Used with permission.

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