Zoisite is a calcium aluminum silicate typically found in metamorphic environments like eclogites and amphibolites. While common in its opaque, green-and-black ruby-in-zoisite form, it is most famous for its transparent blue variety, Tanzanite, which is prized by gem collectors for its strong pleochroism.
Is this zoisite?
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 zoisite with a known reference. Zoisite sits at Mohs 6-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Zoisite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Zoisite typically shows a vitreous to pearly luster.
- 4Match the color rangeCompare against the expected color range: gray, green, pink, brown, blue, yellow.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: prismatic, striated, massive.
Often confused with
Zoisite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Luster reads vitreous to pearly on Zoisite and vitreous on Epidote.
How to tell apart: Luster reads vitreous to pearly on Zoisite and vitreous on Clinozoisite.
How to tell apart: Luster reads vitreous to pearly on Zoisite and vitreous on Tremolite.
Often found alongside zoisite
Minerals reported to co-occur with zoisite. 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
- 6-7
- Density
- 3.1-3.4 g/cm³
- Streak
- White
- Luster
- Vitreous to Pearly
- Transparency
- Translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Prismatic, Striated, Massive
- Cleavage
- Perfect in One Direction
- Rarity
- Common
- Uses
- Gemstone, Lapidary, Collector
- Host rock
- Metamorphic Rocks
- Typical price
- $5-50 for specimens, $10-500+ for gem-quality tanzanite and ruby-in-zoisite
Where rockhounds find zoisite
5 mapped spotsClassic worldwide localities
- Tanzania
- Austria
- Norway
- Kenya
- Pakistan
Field-hunting tip
Look in metamorphic rocks country — that is the host setting where zoisite typically forms. If you start seeing corundum, ruby, garnet in float, you are in the right ground. Field specimens usually show a prismatic, striated, massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Idaho, Maryland, Utah — start trip planning there.
Common questions
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Find zoisite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
