Tanzanite
"Tanzanite is a thousand times rarer than a diamond."
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Tanzanite is the blue/violet variety of the mineral zoisite (a calcium aluminium hydroxyl Sorosilicate) belonging to the epidote group.
The name "tanzanite" was given because the world's only known tanzanite deposit of commercial importance is in northern Tanzania. The name reflects the gem’s limited geographic origin. The mines are all located in an area of about eight square miles in the Merelani Hills, near the base of Mount Kilimanjaro and the city of Arusha.
Although nearly all of the world’s most popular gemstones have been known and used for hundreds of years, tanzanite was not discovered in commercial quantities until the 1960s. In the short time since then, it has become the second most popular blue gem after sapphire.
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Raw tanzanite
Today, nearly all of the gems being sold as "tanzanite" have a blue color that has been enhanced by heating. This treatment is always to be disclosed by the seller.
A small amount of tanzanite in the marketplace has a blue color that was produced naturally through the heat of metamorphism without any treatment by people. This naturally blue, untreated tanzanite is held in very high regard by some gemstone and jewelry buyers who seek it out when making a purchase.
Trivia: Tanzanite is a birthstone for December, along with zircon, turquoise, and blue topaz. Tanzanite is also the gem for a 24th anniversary.
Durability of Tanzanite
Tanzanite is a beautiful gem. In addition to its beauty, it has some properties that require it to be given special care. Tanzanite is best suited for earrings, pendants, and other jewelry items that will not encounter abrasion and impact.
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Hardness is the resistance of a gem to being scratched. Tanzanite has a hardness of about 6.5 on the Mohs Hardness Scale. This hardness is low enough that the gem is vulnerable to being scratched during normal wear if it is used in a ring. This problem can be reduced if the setting is designed to protect the stone from impact and abrasion, or if the ring is not worn during activities when the chance of impact or abrasion is high.
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Toughness is the resistance of a gem to breakage. Tanzanite has one direction of perfect cleavage that could result in the gem being chipped or broken if it receives a sharp impact. Again, settings can be designed to protect the stone, and the owner can avoid wearing the piece during certain activities to reduce the probability of damage. Tanzanite is also sensitive to sudden temperature change and is more subject to breakage at that time.
Color stability in tanzanite is good. Heat-treated stones hold their color and are unlikely to fade under the normal light exposure and in the temperature range of the human environment. As with all gems, contact with acids and other chemicals should be avoided because the stone might be etched or damaged. If cleaning is needed, warm water and a mild soap are recommended. Steam and ultrasonic cleaning are not recommended.