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, 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.