RocksdayGreywacke vs Sandstone
How to tell them apart
A hard, dark 'dirty' sandstone of mixed grains, laid down by underwater avalanches.
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
- Clean sandstone is lighter and grains are more uniform.
Side by side
| Property | Greywacke | Sandstone |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 6–7 | 6–7 |
| Luster | Dull | Dull, gritty |
| Colors | Gray, Black, Green | Brown, Red, Yellow, White, Orange |
| Crystal system / structure | Clastic, poorly sorted | Clastic, sand-sized grains |
| Specific gravity | 2.6–2.8 | 2.2–2.8 |
| Found in | Southern Alps, New Zealand; Wales | Zion and Arches, Utah; Petra, Jordan |
Properties that are the same for both are grayed out.
How to identify greywacke
- Dark gray and very hard.
- Mix of sand grains and rock fragments in fine matrix.
- Breaks into sharp, angular blocks.
Structure: Clastic, poorly sorted
Full Greywacke 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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