Hydrohalite is a rare, unstable hydrated form of common table salt that forms only at temperatures below 0.1°C. Because it dehydrates rapidly into halite when exposed to room temperature, collectors must store specimens in hermetically sealed containers kept in freezing conditions.
Is this hydrohalite?
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 hydrohalite with a known reference. Hydrohalite sits at Mohs 2, 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.
- 4Match the color rangeCompare against the expected color range: colorless, white.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: equant crystals, crusts, or efflorescences.
Often confused with
Hydrohalite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hydrohalite
Minerals reported to co-occur with hydrohalite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- NaCl·2H₂O
- Mohs hardness
- 2
- Density
- 1.605-1.63 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Monoclinic
- Crystal habit
- Equant crystals, crusts, or efflorescences
- Cleavage
- Distinct
- Rarity
- Rare
- Uses
- Collector
- Host rock
- Formed from sea water or in bottom sediments of hypersaline lakes at near-freezing temperatures
Where rockhounds find hydrohalite
Classic worldwide localities
- Hallein, Salzburg, Austria
- Lake Bonney, Taylor Valley, Victoria Land, Antarctica
Field-hunting tip
Where it forms: Formed from sea water or in bottom sediments of hypersaline lakes at near-freezing temperatures. If you start seeing halite, gypsum in float, you are in the right ground. Typical habit: equant crystals, crusts, or efflorescences. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify hydrohalite?+
Where is hydrohalite found?+
What rocks look like hydrohalite?+
What minerals are found with hydrohalite?+
What kind of rock does hydrohalite form in?+
What is hydrohalite used for?+
Find hydrohalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
