RocksdayConglomerate vs Sandstone
How to tell them apart
Rounded pebbles and cobbles glued together by finer sand and cement — a fossil riverbed or beach.
Photo: James St. John, CC BY 2.0
Sand grains — mostly quartz — cemented together. Many sandstones preserve ancient beaches, rivers or desert dunes.
Photo: Unknown, Public domain
Key differences
- Sandstone is sand only, no pebbles.
- Conglomerate contains pebbles, not just sand.
Side by side
| Property | Conglomerate | Sandstone |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 5–7 | 6–7 |
| Luster | Dull | Dull, gritty |
| Colors | Brown, Gray, Red | Brown, Red, Yellow, White, Orange |
| Crystal system / structure | Clastic, rounded pebbles in matrix | Clastic, sand-sized grains |
| Specific gravity | 2.4–2.7 | 2.2–2.8 |
| Found in | Montserrat, Spain; Kata Tjuta, Australia | Zion and Arches, Utah; Petra, Jordan |
Properties that are the same for both are grayed out.
How to identify conglomerate
- Contains rounded pebbles larger than 2 mm.
- Pebbles of different rock types.
- Sand or mud fills the gaps.
- Looks like natural concrete.
Structure: Clastic, rounded pebbles in matrix
Full Conglomerate guide →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 →More comparisons
Could you tell them apart from a blurry close-up?
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