Preiswerkite is a rare trioctahedral mica found primarily in meta-ultramafic rocks. It is most easily identified by its platy habit and occurrence in serpentinite environments, often appearing as pale, micaceous flakes similar to other micas.

Hardness

2.5-3

Mohs

Luster

Pearly

Streak

White

Transparency

Translucent

mineralrareMica Group family

Preiswerkite

Hardness: 2.5-3
Luster: Pearly
Streak: White
Transparency: Translucent

Is this preiswerkite?

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 preiswerkite with a known reference. Preiswerkite sits at Mohs 2.5-3 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Preiswerkite leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Preiswerkite typically shows a pearly luster.
4
Match the color range
Compare against the expected color range: white, colorless, pale yellow.
5
Look at form & habit
Crystal system: monoclinic. Typical habit: platy crystals.

Often confused with

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

Often found alongside preiswerkite

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

All properties

Chemical formula: NaMg₂Al₃Si₂O₁₀(OH)₂
Mohs hardness: 2.5-3
Density: 2.85 g/cm³
Colors: White Colorless Pale Yellow
Streak: White
Luster: Pearly
Transparency: Translucent
Crystal system: Monoclinic
Crystal habit: Platy Crystals
Cleavage: Perfect Basal
Rarity: Rare
Uses: Collector
Host rock: Metamorphic Serpentinite
Typical price: $20-100 per specimen

Where rockhounds find preiswerkite

Classic worldwide localities

Grisons, Switzerland
Val d'Ala, Italy

Field-hunting tip

Look in metamorphic serpentinite country — that is the host setting where preiswerkite typically forms. If you start seeing chlorite, calcite, talc in float, you are in the right ground. Field specimens usually show a platy crystals habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify preiswerkite?+

Mohs hardness is 2.5-3. It typically shows a pearly luster. The streak is white. Common colors include white, colorless, pale yellow.

Where is preiswerkite found?+

Notable localities include Grisons, Switzerland; Val d'Ala, Italy.

How much is preiswerkite worth?+

Typical asking prices fall in the range of $20-100 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like preiswerkite?+

Preiswerkite is most often confused with Muscovite, Paragonite, Margarite. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with preiswerkite?+

Preiswerkite commonly co-occurs with Chlorite, Calcite, Talc, Chromite. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does preiswerkite form in?+

Preiswerkite typically forms in metamorphic serpentinite. Working float back to the host body is the standard way to chase a fresh occurrence.

What is preiswerkite used for?+

Preiswerkite is used in collector.

Find preiswerkite on the map

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