Zoisite (Gem Variety)
Tanzanite
Tanzanite is the blue-violet gem variety of zoisite, and it comes from exactly one place on Earth in gem quality: the Merelani Hills near Mount Kilimanjaro in Tanzania. It's also one of the most recently discovered gemstones in wide commercial use — found only in 1967 and named not for its mineral species but by Tiffany & Co., which recognized its market potential and chose a name tied to its country of origin instead of the more technical 'blue zoisite.'
The geology — what Tanzanite actually is
- Mineral class
- Silicate (a blue-violet variety of zoisite)
- Chemical formula
- Ca2Al3(SiO4)(Si2O7)O(OH)
- Crystal system
- Orthorhombic
- Mohs hardness
- 6 to 7
What causes the color: Trace vanadium produces the blue-to-violet color; in its natural, uncut state the material is strongly trichroic, showing blue, violet, and burgundy-brown tones from three different angles. Heat treatment, applied to nearly all commercial tanzanite, stabilizes the color toward the blue-violet most buyers want and reduces the visible brownish component.
How it forms: Forms in metamorphic rock under specific high-pressure conditions requiring vanadium alongside zoisite's calcium-aluminum silicate chemistry — a combination found in gem quality in only one known location worldwide.
- Merelani Hills, near Mount Kilimanjaro, Tanzania (the only known commercial source in the world)
Treatments & imitations: Near-universally heat-treated at relatively low temperatures to stabilize and enhance the blue-violet color and reduce brownish tones — standard, generally disclosed practice, without which most rough material would show a far less market-desirable brown-green tone.
Real vs. fake: Genuine tanzanite retains noticeable pleochroism/trichroism even after heat treatment, though less pronounced than in untreated rough. It's also notably softer (Mohs 6-7) than sapphire, a similarly-colored blue gem it's sometimes confused with, so cutting and setting need to account for that relative fragility.
The tradition — how people use Tanzanite
Historical use: Tanzanite has essentially no history predating its 1967 discovery — Tiffany & Co. named and marketed it shortly after, choosing to highlight its country of origin rather than its technical mineral name, and it has become one of the fastest-adopted colored gemstones in modern jewelry despite carrying no ancient tradition.
Metaphysical tradition: At the third-eye and crown chakras, modern crystal-healing tradition treats tanzanite as a stone of transformation and spiritual insight, a reputation built entirely within the contemporary crystal and jewelry trade given how recently it was discovered.
How to use it: Rings and pendants are the most typical settings, chosen for its rich blue-violet color.
Cleansing & care: IMPORTANT: moderately soft (Mohs 6-7) with cleavage — avoid ultrasonic cleaners and sharp knocks, and clean gently with mild soap and water instead.
Frequently asked questions
How long can Tanzania's tanzanite supply realistically last?
Geologists who've studied the Merelani deposit have suggested the economically mineable supply could plausibly be exhausted within a few decades at current extraction rates, a genuine concern the gem trade has openly discussed for years, given that no comparable gem-quality vanadium-blue zoisite deposit has been found anywhere else on Earth despite considerable prospecting effort since the 1967 discovery.
How old is tanzanite as a known gemstone?
It was discovered only in 1967, making it one of the most recently identified gemstones in wide commercial use, with no ancient historical tradition predating the late 20th century.
Why was it named tanzanite instead of 'blue zoisite'?
Tiffany & Co., recognizing the stone's market potential after its 1967 discovery, chose to name it after its country of origin, Tanzania, rather than use the more technical mineralogical name — a deliberate marketing decision that stuck.
Related crystals
Sapphire
Corundum Group
Sapphire is corundum in essentially any color other than red — blue is the best known, but pink, yellow, green, and colorless sapphire are all the same mineral species as ruby, just with different trace elements producing different colors. At Mohs 9, it shares ruby's exceptional hardness, and it has one of the longest continuously-documented gem-trading histories on Earth, with Sri Lankan sapphire changing hands for well over 2,000 years.
Iolite
Cordierite (Gem Variety)
Iolite is the gem name for cordierite, and its single most distinctive property is pleochroism taken to an unusual extreme: tilt a piece and it can shift from deep violet-blue to pale yellowish-grey to nearly colorless, three genuinely different colors from three different crystal directions. That property is also why some mineralogists consider cordierite the more scientifically plausible candidate for the legendary Viking navigational 'sunstone' discussed on this site's sunstone page — its pleochroism could, in principle, reveal the sun's polarization angle even through heavy cloud cover.
Labradorite
Feldspar Group
Labradorite is a plagioclase feldspar whose grey, unremarkable-looking base hides a striking optical trick: tilt it and flashes of electric blue, green, gold, or orange sweep across the surface, an effect called labradorescence. That flash comes from the same broad family of phenomena as moonstone's softer glow, but on a coarser internal scale, which is why labradorite produces sharp, switching color flashes instead of a diffuse shimmer. The stone was first described to Western science in 1770 by Moravian missionaries in Labrador, Canada, who learned of it from Inuit communities already using it.
Kyanite
Aluminum Silicate
Kyanite has a genuinely unusual mineralogical claim to fame: it's one of the only common minerals with directional hardness, meaning the same crystal is measurably softer along its length (roughly Mohs 4-4.5) than across it (roughly Mohs 6-7) — a property so distinctive it earned the mineral an old alternate name, disthene, Greek for 'two strengths.' That structural quirk also makes it a genuinely fragile stone to work with despite its blade-like, elegant appearance, and it's a comparatively recent addition to Western gem history, without the millennia-deep documented use of stones like carnelian or lapis lazuli.
Where to buy Tanzanite
We don't have an active affiliate program live yet, so instead of a placeholder link, here's the same buying guidance we'd give a friend.
Specialty mineral dealers & gem shows
The most reliable source for anything beyond common tumbled stones — sellers who specialize in minerals tend to disclose treatments and localities unprompted, because their repeat customers ask.
GIA/AGS-affiliated jewelers
For cut gemstones meant for jewelry (not raw specimens), a seller who can produce or reference an independent lab report (GIA, AGS) removes almost all of the real-vs-fake guesswork.
Marketplace sellers with a track record
Etsy and similar marketplaces host genuine small mineral dealers alongside mislabeled resin castings — check seller reviews specifically for photos of received items, not just star ratings.
Local rock & gem shops
Being able to handle a piece before buying lets you apply the weight and hardness checks described on each stone's own page — something no photo can substitute for.
Whichever seller you choose, ask directly whether the stone is natural or synthetic, and whether it's been treated (heated, dyed, irradiated) — a straightforward answer is the single best signal of a trustworthy seller, more useful than any star rating.
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Sources and factual basis for the geology above: see our methodology.