RocksdayAndesite vs Basalt
How to tell them apart
An intermediate volcanic rock typical of explosive volcanoes above subduction zones.
Photo: Photographer: Siim Sepp, 2005, CC BY-SA 3.0
The most common volcanic rock on Earth. Dark, fine-grained lava that forms the ocean floor and vast lava plains.
Photo: James St. John, CC BY 2.0
Key differences
- Basalt is darker and more uniform.
- Andesite is usually lighter gray with visible white feldspar crystals.
Side by side
| Property | Andesite | Basalt |
|---|---|---|
| Type | Igneous rock | Igneous rock |
| Mohs hardness | 6 | 6 |
| Luster | Dull | Dull |
| Colors | Gray | Black, Gray |
| Crystal system / structure | Porphyritic (crystals in fine groundmass) | Fine-grained (aphanitic) |
| Specific gravity | 2.5–2.8 | 2.9–3.1 |
| Found in | The Andes; Cascade Range, USA | Hawaii; Iceland |
Properties that are the same for both are grayed out.
How to identify andesite
- Medium gray.
- White feldspar crystals and dark specks scattered in a fine-grained base.
- Heavier than rhyolite, lighter than basalt.
- No visible quartz.
Structure: Porphyritic (crystals in fine groundmass)
Full Andesite guide →How to identify basalt
- Dark gray to black and heavy.
- Grains too small to see.
- Often has gas bubbles (vesicles).
- May show six-sided columns in outcrops.
Structure: Fine-grained (aphanitic)
Full Basalt guide →More comparisons
Could you tell them apart from a blurry close-up?
Play today's Rocksday