Tanzanite

Tanzanite is a rare gem variety of the mineral zoisite, which is a mineral in the epidote group.

Tanzanite of commercial importance is only found in the Merelani Hills of Tanzania where it was discovered in 1967.

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TANZANITE (Zoisite) PHYSICAL PROPERTIES

• Tanzanite Chemical composition: Ca₂Al₃O(SiO₄)(Si₂O₇)(OH)
• Class: cyclosilicates
• Crystal System: orthorhombic
• Tanzanite Crystal Habit: tanzanite crystals are prismatic, elongatated on c, striated, also in granular masses
• Tanzanite Twinning: twinning on {100}
• Tanzanite Specific gravity: 3.35
• Index of refraction: 1.691 - 1.700
• Birefringence: weak to mild (0.008 - 0.013)
• Tanzanite Pleochroism: trichroic with strong violet-red/deep blue/yellow-green
  (heating converts the yellow-green component into deep blue leaving only violet-red/deep blue dichroism).
• Hardness: 6-7
• Tanzanite Color: blue, purple, green, yellow, brown, lavender, pink
• Tanzanite Luster: vitreous
• Tanzanite Transparency: transparent
• Cleavage: perfect {010}
• Fracture: uneven, brittle
• Streak: white

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TANZANITE BACKGROUND INFORMATION

The mineral zoisite is a fairly uncommon mineral in the epidote group. The zoisite variety tanzanite is only found in the Merelani Hills of Tanzania where it was discovered in 1967.

The color of tanzanite is due to trace amounts of vanadium and/or chromium impurities in the zoisite structure. When trace amounts of vanadium are present, the tanzanite will change colors from brownish to deep blue when heated as the vanadium oxidizes, yielding the sapphire-like deep blue-violet colors of fine tanzanite gems and fine tanzanite jewelry. Trace amounts of chromium can result in the unheated green natural colors of some rare tanzanite gems if sufficient chromium is present. Heating a natural color brownish tanzanite gem to approximately 500 degrees Celcius is thought to oxidize the V³⁺ to V⁴⁺, thereby eliminating the yellow-brown and/or green colors leaving only the deep blue and violet colors that are the most popular, especially in tanzanite earrings.

Tanzanite is well known for its blue-violet hues, although it also occurs in other colors including shades of pink and green. These different colors are sometimes present as color zoning in the same crystallographic direction. In some tanzanite specimens, these different colors can be present along the direction of one of the three crystallographic axis. Due to the trichroic nature of tanzanite, some very interesting combinations of colors can be present in the same tanzanite crystal or tanzanite gem depending on the direction it is viewed from. For example, there are some tanzanite gems which are green in one direction, blue in another direction, and purple when viewed in a third direction perpendiclur to the green and blue colors!

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TANZANITE GEOLOGIC OCCURRENCE AND DIAGNOSTIC FEATURES

The tanzanite crystals at Merelani, Tanzania, formed within cavities in metamorphic rocks from hydrothermal solutions in contact with gneisses, marbles, and schists.

Tanzanite is usually recognized by its pleochrism, form, index of refraction, and specific gravity.

TANZANITE HISTORICAL INFORMATION AND TANZANITE USES

Tanzanite is a very recently discovered gem material, and so it has no "traditional" information!

The name tanzanite was given to this zoisite variety in 1968 by the New York jeweler Tiffany & Co. in honor of the country where it was discovered in the Merelani Hills near Mount Kilimanjaro. Tanzanite is not the only unique gem material that was discovered relatively recently in this region.

Another rare and desirable gem material with amazing deep green color was also discovered in the same time period in this region by the famous geologist Campbell Bridges. This deep green gem material turned out to be an amazing green garnet. Bridges named this beautiful green garnet tsavorite garnet.

Tanzanite has a hardness of about 6.5 which makes it ideal for use in tanzanite earrings and tanzanite pendants.

Some care should be taken to prevent scratching a tanzanite gem when set into tanzanite rings.

The astrological signs of tanzanite are Sagitarius, Gemini, and Libra.

Tanzanite earrings and other tanzanite jewelry designs are the preferred modern day birthstone gift for birthdays in the month of December.

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TANZANITE METAPHYSICAL PROPERTIES

Wearing tanzanite jewelry or holding a tanzanite crystal is said to facilitate communication on all levels. Tanzanite is also said to promote psychic abilities and to enhance visions of the higher spiritual realms.

Using tanzanite jewelry is also said to be helpful in the treatment of eye and skin disorders.

For more in-depth metaphysical information, see our Metaphysical Books section.

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