RocksdayLimestone vs Sandstone
The quickest way to tell Limestone from Sandstone: Sandstone scratches glass (Mohs 6–7); Limestone can't (Mohs 3–4).
A rock made mostly of calcite, often from shells and skeletons of sea creatures. It dissolves to create caves.
Photo: Mike Davis, CC0
Sand grains — mostly quartz — cemented together. Many sandstones preserve ancient beaches, rivers or desert dunes.
Photo: Unknown, Public domain
Quick tests
- Scratch glass: Sandstone scratches glass (Mohs 6–7); Limestone can't (Mohs 3–4).
- Acid (vinegar or dilute HCl): Limestone fizzes; Sandstone doesn't.
Key differences
- Sandstone is gritty, does not fizz, and the grains rub off.
- Limestone fizzes in acid and is not made of sand grains.
Side by side
| Property | Limestone | Sandstone |
|---|---|---|
| Type | Sedimentary rock | Sedimentary rock |
| Mohs hardness | 3–4 | 6–7 |
| Luster | Dull | Dull, gritty |
| Colors | White, Gray, Brown | Brown, Red, Yellow, White, Orange |
| Crystal system / structure | Varied, often fossiliferous | Clastic, sand-sized grains |
| Specific gravity | 2.5–2.7 | 2.2–2.8 |
| Found in | Bedford, Indiana; Tura, Egypt | Zion and Arches, Utah; Petra, Jordan |
Properties that are the same for both are grayed out.
How to identify limestone
- Fizzes in dilute acid.
- Gray to cream, often with shell fossils.
- A knife scratches it.
- Weathers into smooth, pitted surfaces.
Structure: Varied, often fossiliferous
Full Limestone 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
Frequently asked questions
What is the difference between limestone and sandstone?
Limestone is a sedimentary rock with a Mohs hardness of about 3–4 and a dull luster, usually white, gray or brown. Sandstone is a sedimentary rock with a Mohs hardness of about 6–7 and a dull, gritty luster, usually brown, red, yellow, white or orange.
How can you tell limestone from sandstone?
Sandstone scratches glass (Mohs 6–7); Limestone can't (Mohs 3–4). Limestone fizzes; Sandstone doesn't. Sandstone is gritty, does not fizz, and the grains rub off. Limestone fizzes in acid and is not made of sand grains.
Could you tell them apart from a blurry close-up?
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