igneous
Vesicular Basalt / Scoria
Vesicular Basalt
Hardness: 5-6 (Mohs); Color: Dark brown to dark grey; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific Gravity: 2.8–3.0 but lower apparent density due to pores.
- Hardness
- 5-6 (Mohs)
- Color
- Dark brown to dark grey
- Luster
- Dull/earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark brown to dark grey; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific Gravity: 2.8–3.0 but lower apparent density due to pores.
Formation & geological history
Formed through the rapid cooling of magnesium-rich and iron-rich lava. The holes (vesicles) are created by gas bubbles trapped in the cooling magma as pressure decreases during an eruption.
Uses & applications
Commonly used in landscaping (lava rocks), barbecue grills, high-temperature insulation, and ground cover in construction.
Geological facts
Because of the trapped gas bubbles, scoria can sometimes be light enough to float initially, though it usually sinks faster than pumice because its vesicles are larger and more connected.
Field identification & locations
Identify in the field by its dark color, heavy feel (compared to pumice), and distinctive 'swiss cheese' vesicular texture. It is extremely common in volcanic regions like the Pacific Northwest or Hawaii.
