Anhydrite is an evaporite mineral that differs from gypsum by its lack of water in its chemical structure. It is easily recognized by its three directions of perfect cleavage at right angles, which often cause it to break into distinct cubic fragments.
Is this anhydrite?
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 anhydrite with a known reference. Anhydrite sits at Mohs 3-3.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: white to pale gray.
- 3Read the lusterHold the specimen under a strong light. Luster: pearly on {010}, vitreous to greasy on {001}; vitreous on {100}.
- 4Match the color rangeCompare against the expected color range: colorless, white, gray, blue, violet, reddish, bluish white, violet white, dark gray.
- 5Look at form & habitCrystal system: orthorhombic. Typical habit: massive, plumose.
Often confused with
Anhydrite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Anhydrite is noticeably harder (Mohs 3-3.5 vs. 1.5-2); luster reads pearly on {010}, vitreous to greasy on {001}; vitreous on {100} on Anhydrite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Luster reads pearly on {010}, vitreous to greasy on {001}; vitreous on {100} on Anhydrite and vitreous, pearly on cleavages on Celestine.
How to tell apart: Luster reads pearly on {010}, vitreous to greasy on {001}; vitreous on {100} on Anhydrite and vitreous to resinous, may be pearly on Barite.
Often found alongside anhydrite
Minerals reported to co-occur with anhydrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaSO₄
- Mohs hardness
- 3-3.5
- Density
- 2.98 g/cm³
- Streak
- White to pale gray
- Luster
- Pearly on {010}, vitreous to greasy on {001}; vitreous on {100}
- Transparency
- Transparent to translucent
- Crystal system
- Orthorhombic
- Crystal habit
- Massive, plumose
- Cleavage
- On {010}, perfect; on {100} nearly perfect; on {001} good to imperfect, yielding pseudocubic fragments
- Rarity
- Common
- Uses
- Industrial, Collector, Ornamental
- Host rock
- A major component in sedimentary evaporite deposits and in the cap rocks above salt domes, commonly formed by dehydration of gypsum
Where rockhounds find anhydrite
23 mapped spotsClassic worldwide localities
- Paterson, Passaic Co., New Jersey, USA
- Fairfax quarry, Centreville, Fairfax Co., Virginia, USA
- Carlsbad potash district, Eddy Co., New Mexico, USA
- Boiling Salt Dome, Wharton Co., Texas, USA
- Hall, Tirol, at Ischl and Hallein, Salzburg, and Aussee, Styria, Austria
- Saxony-Anhalt, from Stassfurt-Leopoldshall and Douglashall, near Westeregeln, Germany
U.S. states with anhydrite
Each link opens a state-specific list of mapped rockhounding spots that produce anhydrite.
Field-hunting tip
Where it forms: A major component in sedimentary evaporite deposits and in the cap rocks above salt domes, commonly formed by dehydration of gypsum. If you start seeing gypsum, halite, sylvite in float, you are in the right ground. Typical habit: massive, plumose. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, Wyoming. Start trip planning there.
More anhydrite photos
Common questions
How do you identify anhydrite?+
Where is anhydrite found?+
Can I find anhydrite in the United States?+
What rocks look like anhydrite?+
What minerals are found with anhydrite?+
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Find anhydrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
