Tanzanite is a gemstone named after the East African state of Tanzania, which is the only place in the world where the rare gems are found. A relatively recent discovery, tanzanite's deep blue crystals were first unearthed in 1967 in the Merelani Hills near Arusha, in the foothills of Mount Kilimanjaro. Tanzanite traders are licensed merchants and most are members of the International Colored Gemstone Association. When the first tanzanites were introduced by Tiffany & Co., the precious gems captured the world's attention. The official name of the stone is "blue zoisite," but Tiffany thought the name was too close to the word "suicide," so the name "tanzanite" was proposed. The four factors that are considered when judging tanzanite's quality and cost -- referred to as the Four C's -- are color, clarity, carat weight and cut.
Observe the color: Color is the most important attribute for tanzanite. It is measured by the GIA system, which is universally accepted as the official grading system for colored gems. AAA is the top grade of color, which is a deep saturated blue for tanzanite. AAA is very hard to come by.
Ascertain the clarity: Clarity refers to how "scratch free" the stone is. The GIA system recommends that tanzanite be at least "eye clean" but preferably "loupe clean" (see Resources for a link to the GIA system). VVS stones are top-grade tanzanites, VS gems are characterized by minor scratches, SI1-SI2 gemstones have apparent scratches and I1-I2-I3 are the lowest grade of tanzanite and synonymous with imperfect.
Assess the carat weight: Stones are usually in the 1 to 10+ carat range, and 1 carat is equal to 0.2 grams, which is roughly equivalent to the weight of a paper clip.
Determine the cut: Cut has the least impact on price for tanzanite; however, shapes and cuts are still important. Ovals and emerald cuts are most common.
Beware of blue-violet glass. This is sold as a fake of tanzanite. If you buy tanzanite from a member of the GIA, you will be working with a reputable dealer.
Understand that Block D tanzanite refers to the area from which the stone is mined and that has been known to produce the best-quality tanzanite. The term is synonymous with "top grade."
Make a purchase. Now that you know what you need to consider in valuing this gemstone, contact a dealer through the GIA network. Be sure to request GIA certification on any stones you decide to purchase.