Tanzanite is the blue-violet gem variety of the mineral zoisite, prized for its strong pleochroism that shows blue, violet, and burgundy colors depending on the viewing angle. It is found commercially only in one small area of Tanzania near Mount Kilimanjaro and is usually heat-treated to achieve its signature deep blue color.
Is this tanzanite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch tanzanite with a known reference. Tanzanite sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Tanzanite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Tanzanite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: blue, violet, purple.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic crystals.
Often confused with
Tanzanite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside tanzanite
Minerals reported to co-occur with tanzanite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- Ca₂Al₃(SiO₄)₃(OH)
- Mohs hardness
- 6.5-7
- Density
- 3.35 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic Crystals
- Cleavage
- Perfect in One Direction
- Rarity
- Rare
- Uses
- Gemstone, Collector
- Host rock
- Metamorphic Rocks in Regional Contact Zones
- Typical price
- $200-2000 per carat for high-quality specimens
Where rockhounds find tanzanite
Classic worldwide localities
- Merelani Hills, Tanzania
Field-hunting tip
Look in metamorphic rocks in regional contact zones country — that is the host setting where tanzanite typically forms. If you start seeing graphite, calcite, diopside in float, you are in the right ground. Field specimens usually show a prismatic crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tanzanite?+
Where is tanzanite found?+
How much is tanzanite worth?+
What rocks look like tanzanite?+
What minerals are found with tanzanite?+
What kind of rock does tanzanite form in?+
What is tanzanite used for?+
Find tanzanite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
