Tanzanite is the Secondary Birthstone of December

Tanzanite is a very rare stone which is only found in the foothills of Mount Kilimanjaro in Tanzania.  The fact it is mined in only one location in the world appeals to many.  Legend says that Masai cattle herders in Tanzania noticed that brown zoisite crystals had turned to a deep bluish purple color after being heated from a lightning strike.  This happened only a little over 40 years ago and its popularity has skyrocketed since.  Due to this stone being a such a recent discovery, there is no history or lore surrounding it.  This gem was originally called blue zoisite, but Tiffany & Co introduced it as tanzanite to honor its Tanzanian origin.  The famed company also declared it to be “the most beautiful blue stone to be discovered in 2000 years.”  This stone took its place as December's secondary birthstone, which is the first and only instance the American Gem Society made an addition to the list since its creation in 1912.

For a while, tanzanite was used as a blue sapphire substitute but it quickly developed a reputation of its own.  The best tanzanite comes in rich deep blue color with overtones of intense violet and sometimes burgundy.  This stone is highly pleochroic which means the color it appears changes depending on the direction of view and lighting.  It will show more blue in fluorescent light while displaying more purple in incandescent light.  The cut also plays a large role in the color it displays.  Cutting the stone on the shorter axis results in a bluer color, but produces a lower yield adding to its higher cost.  While a deep color is the most desired, this stone comes in lighter shades as well, that come with a lighter price tag.  Although rare, tanzanite also comes in greenish shades. 

Tanzanite will look much different in rough form, as all tanzanite must be heat treated to achieve its rich color.  The heat treatment process is very tricky.  More heat makes the color deeper, but it will lose its brilliance if too much heat is applied and in this case is “overcooked.”  On the contrary, if it is not heated enough, it will hold higher brilliance, but the color will be too light.  In the past, tanzanite has been sold on cruises for relatively low prices.  We have had clients that purchased some of these tanzanites and bring them in for appraisal.  While the color was dark, they were overcooked, making them very dull with little brilliance.

Unlike many other stones, prices of tanzanite don’t increase in price with higher carat.  Finest quality stones 2-6 carats cost $700-$1000 per carat, larger stones are still within this price range.  This price range depends on quality of cut.

Tanzanite rates a 6 to 7 on the mohs scale.  Precautions should be made against hard blows to the stone as it can crack or break.  It can be used in any jewelry, although gentle wear is advised when placed in rings and not recommended for everyday wear.

Pictured are fine tanzanites 4-6 carats set in 18k gold with diamonds.  Also pictured is a loose 9.8 carat tanzanite which is available for sale.

By Vicky Gulko