Cranswickite is a rare hydrated magnesium sulfate that typically occurs as a secondary mineral in oxidized sulfide deposits. Collectors should look for delicate white fibrous crusts, which are highly sensitive to humidity and must be kept in sealed containers to prevent dehydration.
Is this cranswickite?
3-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 cranswickite with a known reference. Cranswickite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
- 2Match the color rangeCompare against the expected color range: white.
- 3Look at form & habitCrystal system: monoclinic. Typical habit: fibrous, efflorescent crusts.
Often confused with
Cranswickite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside cranswickite
Minerals reported to co-occur with cranswickite. 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
- Density
- 1.917 g/cm³
- Colors
- Transparency
- Translucent
- Crystal system
- Monoclinic
- Crystal habit
- Fibrous, efflorescent crusts
- Rarity
- Rare
- Uses
- Collector
- Host rock
- In veins of up to 3 cm in thickness in a fine-grained metasedimetary rock (illite, quartz, and gypsum)
Where rockhounds find cranswickite
Classic worldwide localities
- Outcrop 1 km east-southeast of Calingasta, Argentina
Field-hunting tip
Where it forms: In veins of up to 3 cm in thickness in a fine-grained metasedimetary rock (illite, quartz, and gypsum). If you start seeing hexahydrite, starkeyite, kieserite in float, you are in the right ground. Typical habit: fibrous, efflorescent crusts. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify cranswickite?+
Where is cranswickite found?+
What rocks look like cranswickite?+
What minerals are found with cranswickite?+
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What is cranswickite used for?+
Find cranswickite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
