Hexahydrite is a fragile, water-soluble sulfate mineral that typically forms as an efflorescence in arid environments or on the walls of mine workings. It is easily recognized by its fibrous white crusts but must be stored in a dry, sealed container to prevent dehydration and crumbling into a powder.
Is this hexahydrite?
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 hexahydrite with a known reference. Hexahydrite sits at Mohs 2-2.5, 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: pearly to vitreous.
- 4Match the color rangeCompare against the expected color range: white, colorless, greenish white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: acicular, encrustations, fibrous.
Often confused with
Hexahydrite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hexahydrite
Minerals reported to co-occur with hexahydrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- MgSO₄·6H₂O
- Mohs hardness
- 2-2.5
- Density
- 1.757 g/cm³
- Streak
- White
- Luster
- Pearly to vitreous
- Transparency
- Transparent to opaque
- Crystal system
- Monoclinic
- Crystal habit
- Acicular, encrustations, fibrous
- Cleavage
- On {100}, perfect
- Rarity
- Common
- Uses
- Collector
- Host rock
- By dehydration of epsomite; as efflorescences on magnesian rock exposures and in mine workings; as speleothems in caves; may be widespread as an evaporative precipitate in saline lakes and soils
Where rockhounds find hexahydrite
Classic worldwide localities
- Oroville, Okanogan Co., Washington, USA
- Campbell mine, Bisbee, Cochise Co. and the San Manuel mine, Pinal Co., Arizona, USA
- Long fibers from the Nevada Dominion adit, Pyramid district, Washoe Co., USA
- Long Park #15 mine, Montrose Co., Colorado, USA
- Bonaparte River between Scottie and Carquill Creeks, Clinton district, British Columbia, Canada
- Rapid Creek, Yukon Territory, Canada
Field-hunting tip
Where it forms: By dehydration of epsomite; as efflorescences on magnesian rock exposures and in mine workings; as speleothems in caves; may be widespread as an evaporative precipitate in saline lakes and soils. If you start seeing epsomite, siderotil in float, you are in the right ground. Typical habit: acicular, encrustations, fibrous. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hexahydrite?+
Where is hexahydrite found?+
What rocks look like hexahydrite?+
What minerals are found with hexahydrite?+
What kind of rock does hexahydrite form in?+
What is hexahydrite used for?+
Find hexahydrite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
