RocksdaySandstone vs Siltstone
How to tell them apart
Sand grains — mostly quartz — cemented together. Many sandstones preserve ancient beaches, rivers or desert dunes.
Photo: Unknown, Public domain
Rock of silt — grains finer than sand but coarser than clay.
Photo: Mike Davis, CC0
Quick tests
- Scratch glass: Sandstone scratches glass (Mohs 6–7); Siltstone can't (Mohs 3–5).
Key differences
- Sandstone grains are visible.
Side by side
| Property | Sandstone | Siltstone |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 6–7 | 3–5 |
| Luster | Dull, gritty | Dull |
| Colors | Brown, Red, Yellow, White, Orange | Gray, Brown, Red |
| Crystal system / structure | Clastic, sand-sized grains | Clastic, silt-sized grains |
| Specific gravity | 2.2–2.8 | 2.4–2.7 |
| Found in | Zion and Arches, Utah; Petra, Jordan | Sedimentary basins worldwide; Grand Canyon (Supai Group) |
Properties that are the same for both are grayed out.
How to identify sandstone
- Gritty, like sandpaper.
- Individual sand grains visible with a lens.
- Grains rub off when scraped.
- Often layered or cross-bedded.
Structure: Clastic, sand-sized grains
Full Sandstone guide →How to identify siltstone
- Grains too small to see but gritty against your teeth.
- Thin layers, not as flaky as shale.
- Dull and earthy.
Structure: Clastic, silt-sized grains
Full Siltstone guide →More comparisons
Could you tell them apart from a blurry close-up?
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