Basalt:
* Composition: A mafic igneous rock, meaning it's rich in magnesium and iron. It's primarily composed of plagioclase feldspar and pyroxene minerals.
* Formation: Formed from rapidly cooled lava, often found in volcanic flows.
* Appearance: Dark grey to black in color, often with a fine-grained texture. Can be vesicular (containing holes from gas bubbles).
Granite:
* Composition: A felsic igneous rock, meaning it's rich in silica and alkali metals. It's composed of quartz, feldspar (both potassium feldspar and plagioclase), and mica.
* Formation: Formed from slowly cooling magma deep underground.
* Appearance: Light-colored (grey, pink, or white), often with a coarse-grained texture. Contains larger, visible crystals.
Obsidian:
* Composition: A volcanic glass. It's formed from rapidly cooled lava with very little crystallization. It's primarily composed of silica, with small amounts of other minerals.
* Formation: Formed from the rapid cooling of lava, usually on the surface of a volcanic flow.
* Appearance: Shiny black, but can be brown, green, or red depending on impurities. Has a glassy, conchoidal fracture (breaks with smooth, curved surfaces).
Here's a table summarizing the differences:
| Feature | Basalt | Granite | Obsidian |
|---|---|---|---|
| Composition | Mafic (rich in magnesium and iron) | Felsic (rich in silica and alkali metals) | Volcanic glass |
| Minerals | Plagioclase feldspar, pyroxene | Quartz, feldspar, mica | Silica with small amounts of other minerals |
| Formation | Rapidly cooled lava | Slowly cooled magma | Rapidly cooled lava |
| Color | Dark grey to black | Light-colored (grey, pink, white) | Shiny black (can be brown, green, red) |
| Texture | Fine-grained | Coarse-grained | Glassy, conchoidal fracture |
In short: Basalt is dark and volcanic, Granite is light and plutonic (formed deep underground), and Obsidian is a glassy, volcanic rock.
