Tanzanite (variety of Zoisite)
Current inventory:  1 gem
 

  
Tanzanite is a Tiffany & Company tradename for the blue-violet variety of Zoisite and named after its country of origin, Tanzania. Zoisite is named after Siegmund Zois (1747-1819), an Austrian scientist.

Discovered in 1967;   IMA status: Not Valid (Discredited by the IMA-CNMNC) (a varity of Zoisite)

Chemistry

Chemical Formula:

Ca₂Al₃Si₃O₁₂(OH)

Calcium Aluminum Silicate Hydroxide

Molecular Weight:

454.36 gm

Composition:

Calcium

17.64 %

Ca

24.68 %

CaO

Aluminum

17.82 %

Al

33.66 %

Al₂O₃

Silicon

18.54 %

Si

39.67 %

SiO₂

Hydrogen

0.22 %

H

1.98 %

H₂O

Oxygen

45.78 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/C.23-100

Nickel-Strunz 10th Ed. ID:

9.BG.10

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO₄ and Si₂O₇ groups; cations in octahedral [6] and greater coordination

Related to:

Epidote Group. Zoisite Subgroup. The orthorhombic dimorph of Clinozoisite. The only orthorhombic member of the Epidote Group.

Members of Group:

Epidote Group: Allanite-(Ce), Allanite-(La), Allanite-(Y), Åskagenite-(Nd), Clinozoisite, Clinozoisite-(Sr), Dissakisite-(Ce), Dissakisite-(La), Dollaseite-(Ce), Epidote, Epidote-(Pb), Epidote-(Sr), Ferriallanite-(Ce), Khristovite-(Ce), Manganiandrosite-(Ce), Manganiandrosite-(La), Manganipiemontite-(Sr), Mukhinite, Piemontite, Piemontite-(Sr), Uedaite-(Ce), Unnamed (Ca-analogue of Manganiandrosite-(La)), Unnamed (La-analogue of Ferriallanite-(Ce)), Unnamed (Mg-analogue of Ferriallanite-(Ce)), Unnamed (Mn-analogue of Ferriallanite-(Ce)), Vanadoandrosite-(Ce), Zoisite

Members of Subgroup:

Zoisite Subgroup: Tanzanite, Thulite, Zoisite

Varieties:

None

Synonyms:

None

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Crystals prismatic, to 10 cm, typically deeply striated || [010] and poorly terminated; columnar to compact, massive.

Twinning:

None

Physical Properties

Cleavage:

Perfect on {010}, Imperfect on {100}

Fracture:

Irregular/Uneven, Conchoidal

Tenacity:

Brittle

Moh's Hardness:

6.0 - 7.0

Density:

3.15 - 3.36 (g/cm³)

Luminescence:

Fluorescent; violet under LW UV

Radioactivity:

Not Radioactive

Optical Properties

Color:

Blue, Purple, Green

Transparency:

Transparent to Translucent

Luster:

Vitreous, Pearly

Refractive Index:

1.692 - 1.700  Biaxial ( + )

Birefringence:

0.009

Dispersion:

0.019

Pleochroism:

Strongly Trichroic; X = pale pink to red-violet; Y = nearly colorless to bright pink or deep blue; Z = pale yellow to yellow-green.

Occurances

Geological Setting:

Typically in medium-grade regionally metamorphosed crystalline schists formed from igneous, sedimentary, or metamorphic rocks relatively high in calcium; in eclogites and blueschist facies metamorphic rocks.

Common Associations:

Albite, Biotite, Calcite, Garnet, Hornblende, Quartz

Common Impurities:

Fe, Mn, Mg, Cr, Ti, Ca, Na, V, Sr, H₂O

Type Locality:

Merelani Hills, Umba Valley, Lelatema Mts, Arusha Region, Tanzania

Year Discovered:

1967

View mineral photos:

Tanzanite Mineral Photos and Locations

More Information

Mindat.org (Tanzanite)
Mindat.org (Zoisite)
Webmineral.com (Zoisite)

The name "Tanzanite" is a tradename, not an officially recognized mineral. It was named in the 1960's by Tiffany and Company after Tanzania, its country of origin. It is a variety of Zoisite which is a member of the Epidote group of minerals that includes Allanite, Clinozoisite, Epidote, Hancockite, Mukhinite, Piemontite, Tanzanite, Thulite and Zoisite. It has become the most popular gemstone after Diamond, Ruby, Sapphire and Emerald.

The gem Tanzanite is the result of (usually) heating green to brown Zoisite to about 500 - 600 degrees Farenheit. When this occurs, the greenish to brownish Zoisite transforms into the characteristic intense blue with violet dichroism of Tanzanite. Unheated Zoisite gems are available in shades of green, yellow, brown, gold, pink, and very rarely blue or violet. Tanzanite is strongly dichroic, showing different shades of blues and violets depending on lighting conditions and viewing angle. It will show the most blue under daylight and more violet under incandescent light. Despite its popularity in jewelry, Tanzanite is a relatively soft and brittle gem and should be worn with care.

It is believed that Tanzanite was first discovered by the Masai tribe in the Merelani Hills in northern Tanzania after a grass fire changed the brownish Zoisite crystals on the ground to blue-violet. Then in the 1960's a Portuguese geologist named DeSouza brought these blue-violet crystals to the attention of Tiffany and Company. Until recent very small finds in Kenya, the only source of Tanzanite was the Merelani Hills, Umba Valley, Lelatema Mountains, Arusha Region in northern Tanzania.
 

  
Tanzanite gems for sale: