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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, pearly on cleavage.
- 4Match the color rangeCompare against the expected color range: gray, green, pink, brown, blue, yellow, apple green, rose red.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: columnar, prismatic, striated.
Often confused with
Zoisite vs. its common look-alikes, and how to tell them apart in the field.
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
- 3.15-3.36 g/cm³
- Streak
- White
- Luster
- Vitreous, pearly on cleavage
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Columnar, prismatic, striated
- Cleavage
- {010}, perfect; {100}, imperfect
- Rarity
- Common
- Uses
- Gemstone, Lapidary, Collector
- Host rock
- Typically in medium-grade regionally metamorphosed crystalline schists formed from igneous, sedimentary, or metamorphic rocks relatively high in calcium; in eclogites and blueschist facies metamorphic rocks
Where rockhounds find zoisite
5 mapped spotsClassic worldwide localities
- Goshen and Williamsburg, Hampshire Co., Massachusetts, USA
- Keystone quarry, near Cornog, Chester Co., Pennsylvania, USA
- Milford Heights, Baltimore Co., Maryland, USA
- Spruce Pine, Mitchell Co., North Carolina, USA
- Saualpe, Carinthia, and in the Zillertal, Tirol, Austria
- Trondheim, Norway
Field-hunting tip
Where it forms: Typically in medium-grade regionally metamorphosed crystalline schists formed from igneous, sedimentary, or metamorphic rocks relatively high in calcium; in eclogites and blueschist facies metamorphic rocks. If you start seeing garnet, albite, biotite in float, you are in the right ground. Typical habit: columnar, prismatic, striated. 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
How do you identify zoisite?+
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Can I find zoisite in the United States?+
What rocks look like zoisite?+
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Find zoisite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
