Tanzanite
Chemical formula: Ca₂Al₃(SiO₄)₃(OH)
Tanzanite is a blue-violet variety of zoisite, prized in jewelry for its unique pleochroism and intense color.
Description
## Characteristics Tanzanite is a variety of the mineral zoisite, a calcium aluminum silicate, characterized by its exceptional blue-violet color. Typical tanzanite specimens display an intense color that can range from sapphire blue to amethyst violet, often with visible reddish hues. Its beauty stems from strong pleochroism, which is the ability to display different colors depending on the viewing angle. Tanzanite crystals are usually elongated, with a prismatic or tabular habit, often with distinct striations on their faces. ## Physical Properties Tanzanite's hardness on the Mohs scale is 6-7, making it relatively scratch-resistant, though it requires careful handling during use. This mineral exhibits a vitreous luster. It is transparent to translucent. The density of tanzanite is approximately 3.35 g/cm³. ## Colors and Varieties The most desirable tanzanite color is an intense, deep blue with a violet overtone. This color is often the result of heat treatment, which transforms naturally occurring brownish-green or yellowish crystals into the desired blue and violet hues. Without heat treatment, tanzanite can occur in greenish, yellow, or brownish shades. ## History and Name Tanzanite was discovered in 1967 in Tanzania, in the Arusha region. The name "tanzanite" was given by Tiffany & Co., which introduced this gemstone to the jewelry market, referencing its country of origin. Prior to the discovery of tanzanite, blue varieties of zoisite were practically unknown. ## Uses Tanzanite is primarily a prized gemstone. Its unique color and pleochroism make it suitable for use in jewelry such as rings, necklaces, earrings, and bracelets. Due to its rarity and beauty, it is sought after by mineral collectors.
Diagnostic features
## Identification Tanzanite can be identified by its characteristic blue-violet color and strong pleochroism, which manifests as a color change depending on the viewing angle. It often exhibits three colors: blue, violet, and reddish. Its hardness on the Mohs scale is 6-7. ## Distinguishing from Similar Minerals Tanzanite can be confused with sapphire, ametrine, or iolite. It differs from sapphire by its lower hardness and stronger pleochroism. Ametrine is quartz, which has a different crystal structure and lacks pleochroism. Iolite also exhibits pleochroism, but its colors are usually less intense and more grayish than in tanzanite. ## Crystal Forms Tanzanite occurs as elongated, prismatic, or tabular crystals. It often forms granular or massive aggregates.
Geological environment
## Genesis Tanzanite forms under conditions of regional and contact metamorphism, in calcium-rich rocks such as marbles and calc-silicate rocks. It occurs in hydrothermal deposits, where solutions rich in trace elements, such as vanadium, contribute to its characteristic coloration. ## Mineral Associations Tanzanite often co-occurs with minerals such as graphite, pyrite, quartz, prehnite, calcite, and diopside. ## Locations The only known commercial source of tanzanite is the Merelani Hills area in northern Tanzania, near the city of Arusha. These deposits are located at the foot of Mount Kilimanjaro.
Rarity
Very Rare
Collector aspects
## Quality Criteria The most important quality criteria for tanzanite are the intensity and saturation of color, clarity, and absence of inclusions. Stones with a deep, vivid blue-violet color are most highly valued. Large, clean specimens with excellent cuts are particularly sought after. ## Market Prices Tanzanite prices vary widely and depend on many factors, such as color, clarity, cut, and carat weight. The highest quality, large stones command significantly higher prices per carat. Smaller specimens with less intense color are more affordable. ## Popular Localities All commercial tanzanites originate from a single region in Tanzania, the Merelani Hills. Specimens from this location are prized for their unique properties and beauty.
Care and storage
## Cleaning Tanzanite should be cleaned gently, using warm water with mild soap and a soft brush. After washing, the stone should be thoroughly rinsed with clean water to remove any soap residue, then dried with a soft cloth. ## What to Avoid Avoid cleaning tanzanite in ultrasonic cleaners and steam cleaners, as they can damage the stone or weaken its setting. Tanzanite is sensitive to sudden temperature changes, strong impacts, and contact with chemicals such as acids or solvents. Prolonged exposure to direct sunlight can also negatively affect its color. ## Storage Tanzanite should be stored separately from other gemstones and jewelry to prevent scratching. It is best to store it in a soft pouch or a separate compartment in a jewelry box, in a dry and cool place, away from sources of light and heat.