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, 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.
