igneous
Scoria (Lava Rock)
Scoria
Hardness: 5-6 on Mohs scale; Color: Dark red, reddish-brown to black; Luster: Dull, earthy; Texture: Highly vesicular (pitted with gas bubbles); Specific Gravity: Low (often floats briefly before sinking)
- Hardness
- 5-6 on Mohs scale
- Color
- Dark red, reddish-brown to black
- Luster
- Dull, earthy
Identified More igneous →
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Physical properties
Hardness: 5-6 on Mohs scale; Color: Dark red, reddish-brown to black; Luster: Dull, earthy; Texture: Highly vesicular (pitted with gas bubbles); Specific Gravity: Low (often floats briefly before sinking)
Formation & geological history
Formed during explosive volcanic eruptions when gas-rich mafic to intermediate lava cools rapidly, trapping expanding gas bubbles inside the solidifying rock.
Uses & applications
Widely used in landscaping as drainage layer, in gas grills as heat conductors, in lightweight concrete aggregate, and as decorative lava stone.
Geological facts
Because it cools so rapidly under low pressure, scoria traps thousands of tiny gas bubbles, creating a sponge-like texture that makes the rock very lightweight.
Field identification & locations
Identified by its distinctive porous, dark red or black sponge-like texture and light weight. Commonly found near active or extinct volcanic fields, cinder cones, and lava flows.
