Claystone is a fine-grained, non-fissile sedimentary rock composed primarily of clay-sized particles. Unlike shale, it does not display fissility or splitting along thin parallel laminations and often feels smooth or powdery to the touch when dry.

Hardness

1-2

Mohs

Luster

Dull

Streak

White

Transparency

Opaque

sedimentarycommon

Claystone

Hardness: 1-2
Luster: Dull
Streak: White
Transparency: Opaque

Is this claystone?

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 claystone with a known reference. Claystone sits at Mohs 1-2 — softer than the next harder reference, harder than the previous one.
2
Check the streak
Drag the specimen across an unglazed porcelain plate. Claystone leaves a white streak.
3
Read the luster
Hold the specimen under a strong light. Claystone typically shows a dull luster.
4
Match the color range
Compare against the expected color range: gray, brown, red, yellow, black.
5
Look at form & habit
Typical habit: massive.

Often confused with

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

How to tell apart: Siltstone is the harder of the two (Mohs 3-4 vs. 1-2).

Often found alongside claystone

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

All properties

Mohs hardness: 1-2
Density: 2.0-2.6 g/cm³
Colors: Gray Brown Red Yellow Black
Streak: White
Luster: Dull
Transparency: Opaque
Crystal habit: Massive
Cleavage: None
Rarity: Common
Uses: Industrial, Geological Study
Host rock: Sedimentary Basins
Typical price: low, generally available as bulk specimen material

Where rockhounds find claystone

Classic worldwide localities

worldwide
Kentucky, USA
London Basin, UK
Paris Basin, France

Field-hunting tip

Look in sedimentary basins country — that is the host setting where claystone typically forms. If you start seeing quartz, feldspar, calcite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop.

Common questions

How do you identify claystone?+

Mohs hardness is 1-2. It typically shows a dull luster. The streak is white. Common colors include gray, brown, red, yellow.

Where is claystone found?+

Notable localities include worldwide; Kentucky, USA; London Basin, UK; Paris Basin, France.

How much is claystone worth?+

Typical asking prices fall in the range of low, generally available as bulk specimen material. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like claystone?+

Claystone is most often confused with Shale, Siltstone, Mudstone. A quick hardness test and a streak check separate the look-alikes faster than color alone.

What minerals are found with claystone?+

Claystone commonly co-occurs with Quartz, Feldspar, Calcite, Mica. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does claystone form in?+

Claystone typically forms in sedimentary basins. Working float back to the host body is the standard way to chase a fresh occurrence.

What is claystone used for?+

Claystone is used in industrial, geological study.

Find claystone on the map

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