Polyhalite is a complex evaporite mineral found primarily in marine sedimentary deposits. It is often identified by its characteristic brick-red to pinkish color caused by iron oxide inclusions and its occurrence in massive, granular, or fibrous aggregates within salt beds.
Is this polyhalite?
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 polyhalite with a known reference. Polyhalite sits at Mohs 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.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous to resinous.
- 4Match the color rangeCompare against the expected color range: colorless, gray, gray white, white, pink.
- 5Look at form & habitCrystal system: triclinic. Typical habit: massive.
Often confused with
Polyhalite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Polyhalite is noticeably harder (Mohs 3.5 vs. 1.5-2); luster reads vitreous to resinous on Polyhalite and subvitreous, pearly on {010} cleavages, silky if fibrous on Gypsum.
How to tell apart: Luster reads vitreous to resinous on Polyhalite and pearly on {010}, vitreous to greasy on {001}; vitreous on {100} on Anhydrite.
How to tell apart: Polyhalite is noticeably harder (Mohs 3.5 vs. 2-2.5).
Often found alongside polyhalite
Minerals reported to co-occur with polyhalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- K₂Ca₂Mg(SO₄)₄·2H₂O
- Mohs hardness
- 3.5
- Density
- 2.78 g/cm³
- Streak
- White
- Luster
- Vitreous to resinous
- Transparency
- Transparent
- Crystal system
- Triclinic
- Crystal habit
- Massive
- Cleavage
- On {101}, perfect; on {010}, a parting
- Rarity
- Common
- Uses
- Industrial, Fertilizer, Collector
- Host rock
- Common in marine salt deposits, where it may constitute the major component, present in billion-ton amounts; diagenetic in playa muds, formed from gypsum in the presence of Mg–K-rich solutions
Where rockhounds find polyhalite
3 mapped spotsClassic worldwide localities
- Carlsbad potash district, Eddy Co., and adjacent parts, Texas, USA
- Paradox Basin, Grand Co., Utah, USA
- Ischl, Bad Aussée, and Altaussée, Upper Austria
- Hallstatt, Styria, Austria
- Hall, Tirol, Austria
- Stassfurt-Westeregeln district, Saxony-Anhalt, and at Berchtesgaden, Bavaria, Germany
Field-hunting tip
Where it forms: Common in marine salt deposits, where it may constitute the major component, present in billion-ton amounts; diagenetic in playa muds, formed from gypsum in the presence of Mg–K-rich solutions. If you start seeing halite, anhydrite, glauberite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, Nevada. Start trip planning there.
Common questions
How do you identify polyhalite?+
Where is polyhalite found?+
Can I find polyhalite in the United States?+
What rocks look like polyhalite?+
What minerals are found with polyhalite?+
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Find polyhalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
