Siltstone is a fine-grained sedimentary rock composed mainly of silt-sized particles. It feels gritty to the touch compared to claystone or shale and is commonly found in river channels, deltas, and floodplains.

Hardness

3-4

Mohs

Luster

Dull

Streak

White

Transparency

Opaque

sedimentarycommon

Siltstone

Hardness: 3-4
Luster: Dull
Streak: White
Transparency: Opaque

Is this siltstone?

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

Often confused with

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

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

Often found alongside siltstone

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

All properties

Mohs hardness: 3-4
Density: 2.2-2.6 g/cm³
Colors: Gray Red Brown Tan Green
Streak: White
Luster: Dull
Transparency: Opaque
Crystal habit: Massive
Cleavage: None
Rarity: Common
Uses: Construction, Decorative, Educational
Host rock: Sedimentary Basins
Typical price: $1-10 per specimen

Where rockhounds find siltstone

Classic worldwide localities

USA
United Kingdom
Germany
China
Australia

Field-hunting tip

Look in sedimentary basins country — that is the host setting where siltstone typically forms. If you start seeing quartz, clay minerals, 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 siltstone?+

Mohs hardness is 3-4. It typically shows a dull luster. The streak is white. Common colors include gray, red, brown, tan.

Where is siltstone found?+

Notable localities include USA; United Kingdom; Germany; China; Australia.

How much is siltstone worth?+

Typical asking prices fall in the range of $1-10 per specimen. Quality, size, and provenance can move individual specimens well outside that range.

What rocks look like siltstone?+

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

What minerals are found with siltstone?+

Siltstone commonly co-occurs with quartz, clay minerals, calcite, feldspar. Spotting any of these in float or country rock is a useful trip signal.

What kind of rock does siltstone form in?+

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

What is siltstone used for?+

Siltstone is used in construction, decorative, educational.

Find siltstone on the map

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