RocksdaySandstone vs Tuff
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 made of compacted volcanic ash, often soft enough to carve.
Photo: Ivan Fernanadez 1011, CC BY-SA 4.0
Quick tests
- Scratch glass: Sandstone scratches glass (Mohs 6–7); Tuff can't (Mohs 3–5).
Key differences
- Sandstone grains are rounded sand, not volcanic shards.
Side by side
| Property | Sandstone | Tuff |
|---|---|---|
| Type | Sedimentary rock | Igneous rock |
| Mohs hardness | 6–7 | 3–5 |
| Luster | Dull, gritty | Dull |
| Colors | Brown, Red, Yellow, White, Orange | White, Gray, Pink, Brown |
| Crystal system / structure | Clastic, sand-sized grains | Pyroclastic (volcanic ash) |
| Specific gravity | 2.2–2.8 | 1.5–2.5 |
| Found in | Zion and Arches, Utah; Petra, Jordan | Cappadocia, Turkey; Rapa Nui (Easter Island) |
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 tuff
- Light, porous and often crumbly.
- Gritty with fragments of pumice, crystals and rock.
- Pale colors; may show layering.
Structure: Pyroclastic (volcanic ash)
Full Tuff guide →More comparisons
Could you tell them apart from a blurry close-up?
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