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. Tachyhydrite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Tachyhydrite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellow, orange.
- 5Look at form & habitCrystal system: trigonal. Typical habit: massive, granular, or rarely as indistinct crystals.
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
- 1.67 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Trigonal
- Crystal habit
- Massive, Granular, Or Rarely as Indistinct Crystals
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Collector, Scientific Research
- Host rock
- Evaporite Deposits
- Typical price
- $10-50 per specimen
Where rockhounds find tachyhydrite
Classic worldwide localities
- Stassfurt, Germany
- Sondershausen, Germany
- Werra, Germany
- Carlsbad, New Mexico, USA
Field-hunting tip
Look in evaporite deposits country — that is the host setting where tachyhydrite typically forms. If you start seeing halite, sylvite, carnallite in float, you are in the right ground. Field specimens usually show a massive, granular, or rarely as indistinct crystals habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find tachyhydrite on the map
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