Tachyhydrite is a very rare and highly deliquescent halide mineral primarily found in saline evaporite deposits. Due to its extreme sensitivity to moisture, it must be stored in a sealed container to prevent it from turning into a liquid brine.
Is this tachyhydrite?
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 tachyhydrite with a known reference. Tachyhydrite 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, yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: deliquescent, massive, tastes bitter.
Often confused with
Tachyhydrite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside tachyhydrite
Minerals reported to co-occur with tachyhydrite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- CaMg₂Cl₆·12H₂O
- Mohs hardness
- 2
- Density
- 1.667 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Deliquescent, massive, tastes bitter
- Cleavage
- {1011}, perfect
- Rarity
- Uncommon
- Uses
- Collector, Scientific research
- Host rock
- A rare mineral in bedded salt deposits of oceanic origin
Where rockhounds find tachyhydrite
Classic worldwide localities
- Stassfurt, 34 km south of Magdeburg, Saxony-Anhalt, at Krügershall-Teutschenthal, near Halle, and from Vienenburg, Lower Saxony, Germany
- Santa Rosa de Lima and Taquari Basins, Sergipe, Brazil, with reserves estimated at 4 billion t
- Khorat Plateau, Thailand, also massive reserves
Field-hunting tip
Where it forms: A rare mineral in bedded salt deposits of oceanic origin. If you start seeing kainite, carnallite, sylvite in float, you are in the right ground. Typical habit: deliquescent, massive, tastes bitter. Train your eye for that shape before scanning the outcrop.
Common questions
How do you identify tachyhydrite?+
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What rocks look like tachyhydrite?+
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Find tachyhydrite on the map
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