Starkeyite is an unstable, hydrated magnesium sulfate mineral that typically forms as an efflorescent crust in dry environments. It is highly susceptible to dehydration, often altering to hexahydrite or epsomite if exposed to humidity, requiring careful storage in sealed containers to preserve its structural integrity.
Is this starkeyite?
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 starkeyite with a known reference. Starkeyite sits at Mohs 2-3, 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: dull.
- 4Match the color rangeCompare against the expected color range: white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, efflorescent crusts, granular.
Often confused with
Starkeyite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull on Starkeyite and vitreous, silky in fibrous aggregates on Epsomite.
How to tell apart: Luster reads dull on Starkeyite and pearly to vitreous on Hexahydrite.
How to tell apart: Luster reads dull on Starkeyite and vitreous, silky if fibrous on Goslarite.
Often found alongside starkeyite
Minerals reported to co-occur with starkeyite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgSO₄·4H₂O
- Mohs hardness
- 2-3
- Density
- 2.01 g/cm³
- Colors
- Streak
- White
- Luster
- Dull
- Transparency
- Semitransparent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, efflorescent crusts, granular
- Cleavage
- Perfect
- Rarity
- Rare
- Uses
- Collector
- Host rock
- An uncommon secondary mineral formed in the presence of iron sulfides; as efflorescences from evaporation of surface and ground waters
Where rockhounds find starkeyite
Classic worldwide localities
- Starkey mine, Madison Co., Missouri, USA
- Alta troilite mine, Del Norte Co., California, USA
- Green River Formation, northern Piceance Creek Basin, Garfield and Rio Blanco Cos., and at Garden Park, Fremont Co., Colorado, USA
- Goldstrike mine, Lynn district, Eureka Co., Nevada, USA
- Hansa I mine, Empelde, and the Niedersachsen mine, near Wathlingen, Lower Saxony, Germany
- Nižná Mysl’a mine, Vel’ky Milic massif, Slovakia
Field-hunting tip
Where it forms: An uncommon secondary mineral formed in the presence of iron sulfides; as efflorescences from evaporation of surface and ground waters. If you start seeing pyrite, marcasite, konyaite in float, you are in the right ground. Typical habit: fibrous, efflorescent crusts, granular. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify starkeyite?+
Where is starkeyite found?+
What rocks look like starkeyite?+
What minerals are found with starkeyite?+
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What is starkeyite used for?+
Find starkeyite on the map
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