Hydrotalcite is a layered double hydroxide mineral typically forming soft, waxy or pearly masses and thin hexagonal plates. It is most commonly identified by its low hardness and association with serpentinite or contact-metamorphosed carbonate rocks. Collectors look for its characteristic micaceous habit and smooth, greasy feel.

Hardness

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineralcommonHydrotalcite Group family

Hydrotalcite

Hardness: 2
Luster: Pearly
Streak: White
Transparency: Translucent

Is this hydrotalcite?

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 hydrotalcite with a known reference. Hydrotalcite 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. Hydrotalcite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Hydrotalcite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: white, gray, pale green, pale yellow.
5
Look at form & habit
Crystal system: trigonal. Typical habit: tabular crystals, micaceous aggregates, massive.

Often confused with

Hydrotalcite vs. its common look-alikes, and how to tell them apart in the field.

mineral

Talc

Mohs 1

How to tell apart: Hydrotalcite is noticeably harder (Mohs 2 vs. 1).

Often found alongside hydrotalcite

Minerals reported to co-occur with hydrotalcite. Spotting these in float or country rock is a strong cue you are in the right ground.

All properties

Chemical formula: Mg₆Al₂CO₃(OH)₁₆·4H₂O
Mohs hardness: 2
Density: 2.06-2.10 g/cm³
Colors: White Gray Pale Green Pale Yellow
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Trigonal
Crystal habit: Tabular Crystals, Micaceous Aggregates, Massive
Cleavage: Perfect Basal
Rarity: Common
Uses: Collector, Scientific Research
Host rock: Metamorphosed Limestones and Dolomites, Ultramafic Rocks
Typical price: $10-50 thumbnail

Where rockhounds find hydrotalcite

Classic worldwide localities

Snarum, Norway
Bergslagen, Sweden
Ural Mountains, Russia
Val di Susa, Italy
Amity, New York, USA

Field-hunting tip

Look in metamorphosed limestones and dolomites, ultramafic rocks country, the host setting where hydrotalcite typically forms. If you start seeing brucite, dolomite, calcite in float, you are in the right ground. Field specimens usually show a tabular crystals, micaceous aggregates, massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify hydrotalcite?+

Mohs hardness is 2. It typically shows a pearly luster. The streak is white. Common colors include white, gray, pale green, pale yellow.

Where is hydrotalcite found?+

Notable localities include Snarum, Norway; Bergslagen, Sweden; Ural Mountains, Russia; Val di Susa, Italy; Amity, New York, USA.

How much is hydrotalcite worth?+

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

What rocks look like hydrotalcite?+

Hydrotalcite is most often confused with Talc, Brucite, Pyrophyllite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with hydrotalcite?+

Hydrotalcite commonly co-occurs with Brucite, Dolomite, Calcite, Magnesite, Serpentine. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does hydrotalcite form in?+

Hydrotalcite typically forms in metamorphosed limestones and dolomites, ultramafic rocks. Working float back to the host body is the standard way to chase a fresh occurrence.

What is hydrotalcite used for?+

Hydrotalcite is used in collector, scientific research.

Find hydrotalcite on the map

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