Discovering Tanzanite: The Lightning Stone

Designated as a birthstone for December by the American Gem Association in 2002, Tanzanite is a rare violet-blue gemstone of the zoisite family, found only in Tanzania in central Africa. Only discovered in 1967 by Maasai tribesmen, what this remarkable gemstone lacks in ancient history, it more than makes up for with an enchanting origin story and rapid popularity growth.

An Origin Story fuelled by Lightning

In 1967 violent thunderstorms hit the hills around Mount Kilimanjaro. The lightning caused bush fires, which in turn caused the Maasai who lived there to flee. On their return they were surprised to discover bright blue gemstones in the scorched earth that weren’t there before.

Unable to identify these mystery stones, they were sent to a gemologist, who sent them to the GIA (the Gemological Institute of America) where it was discovered that these gems were a previously undiscovered form of blue zoisite (previously only found as a brownish gemstone).

It transpired that the heat from the fires had caused the usually unassuming brownish zoisite gemstones to turn a bright sparkling blue/purple, and thus the Tanzanite was discovered.

The Origins and Formation of Tanzanites

Geological Formation

Tanzanite was formed millions of years ago when the movement of tectonic plates around the base of Mount Kilimanjaro caused intense pressure and high temperatures, which caused the crystallisation of zoisite and therefore the creation of Tanzanite.

Colour & Pleochroism

Tanzanite owes its beautiful colour to the trace elements vanadium and chromium, and while primarily known for its blue-violet colour, it can also show shades of purple, blue, and burgundy depending on the lighting conditions and angle of view. Tanzanite is also one of very few pleochroic gemstones, meaning it can appear to be different colors when viewed from different angles. This can make it appear blue from one angle and violet from another.

Heat Treatment

Almost all Tanzanite on the commercial market is heat treated. As we discovered from its origin story, in its natural state Tanzanite often appears brownish, which is caused by the red and yellow hues in the natural crystals, but when heated to between 400C and 600C the red and yellow components disappear revealing the signature beautiful blues and purples of Tanzanites. It’s worth noting though that unlike many other gemstones, the heat treating of Tanzanites does not negatively affect its commercial value.

Scarcity Value

Tanzanite is already considered one of the rarest gemstones in the world as it is found in only one location: the Merelani Hills of Tanzania. It is anticipated that because Tanzanite is only found in a limited geographical area, the supply will eventually diminish leading to increased rarity and value over time.

18ct Gold, Silver, Rosecut Tanzanite Rings 

The Cultural Significance of Tanzanites

As Tanzanites are a relatively modern gemstone, they don’t have much to tell us in the way of historical myth and legend, however as a single origin gemstone it boasts strong cultural significance for the Maasai people of Tanzania.

A Gift from God

The Maasai people, indigenous to the region where Tanzanite is mined, and discoverers of the gem, have a deep cultural connection to the land. They believe tanzanites to be a gift from God as the colour blue is sacred for them.

Wealth, Health and long life

Tanzanite is often viewed as a symbol of wealth and prosperity. The gemstone's vivid colour and rarity make it a desirable, and it is sometimes given as a gift to signify status.

Tanzanian mothers are traditionally given tanzanite to wear during childbirth, because the Maasai believed the stone could bring health and a long life to babies.

Tanzanites in History

Tiffany and Co.

In the late 1960s Tiffany & Co. played a crucial role in popularising Tanzanite. Believing its original name “Blue Zoisite” not to be commercial enough, the company renamed the stone "Tanzanite" and began marketing it as a rare and precious gemstone.

“The Heart of the Ocean”

While the famed necklace in the 1997 movie Titanic, known as “The Heart of the Ocean” was depicted as a blue diamond, it was actually a 28 carat heart-shaped Tanzanite.

The World’s Largest Tanzanite

The world’s largest cut tanzanite comes in at a huge 703.4 carats is called L’Heure Bleu and was carved by New York based artist Naomi Sarna. The piece, mounted on a sterling silver base was recognised by Guinness World Records in March 2024.