igneous
Vesicular Basalt
Extrusive mafic igneous rock; primarily (Ca,Na)(Mg,Fe,Al,Si)2O6 (Pyroxene) and (Ca,Na)Al(Al,Si)Si2O8 (Plagioclase Feldspar)
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The pitted texture (vesicles) occurs as gas bubbles are trapped in the cooling lava. Most found on Earth is from the Cenozoic era or younger due to plate tectonics.
Uses & applications
Used extensively as aggregate in construction, road base, concrete, and railroad ballast. Highly vesicular specimens (like scoria) are used in landscaping and as abrasive 'pumice stones' in cosmetics.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found in abundance on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and the circular or almond-shaped pits on the surface. Commonly found in volcanic fields, oceanic islands (like Hawaii), and mid-ocean ridges.
