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 — that is 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.