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.

Hardness

Mohs

Luster

Vitreous

Streak

White

Transparency

Transparent

mineraluncommon

Tachyhydrite

Hardness: 2
Luster: Vitreous
Streak: White
Transparency: Transparent

Is this tachyhydrite?

5-step field check

Run through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.

1
Test the hardness
Try to scratch tachyhydrite with a known reference. Tachyhydrite sits at Mohs 2, softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Tachyhydrite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Tachyhydrite typically shows a vitreous luster.
4
Match the color range
Compare against the expected color range: colorless, white, yellow, orange.
5
Look at form & habit
Crystal 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
Colors: Colorless White Yellow Orange
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, 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

How do you identify tachyhydrite?+

Mohs hardness is 2. It typically shows a vitreous luster. The streak is white. Common colors include colorless, white, yellow, orange.

Where is tachyhydrite found?+

Notable localities include Stassfurt, Germany; Sondershausen, Germany; Werra, Germany; Carlsbad, New Mexico, USA.

How much is tachyhydrite worth?+

Typical asking prices fall in the range of $10-50 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like tachyhydrite?+

Tachyhydrite is most often confused with Carnallite, Bischofite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with tachyhydrite?+

Tachyhydrite commonly co-occurs with Halite, Sylvite, Carnallite, Anhydrite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does tachyhydrite form in?+

Tachyhydrite typically forms in evaporite deposits. Working float back to the host body is the standard way to chase a fresh occurrence.

What is tachyhydrite used for?+

Tachyhydrite is used in collector, scientific research.

Find tachyhydrite on the map

RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.