igneous
Scoria (Lava Rock)
Scoria (extrusive volcanic rock)
Hardness: 5-6 (Mohs scale); Color: Black, dark gray, or reddish-brown; Luster: Dull or submetallic; Structure: Highly vesicular (full of holes); Cleavage: None; Specific Gravity: Low (1.2 - 2.0).
- Hardness
- 5-6 (Mohs scale)
- Color
- Black, dark gray, or reddish-brown
- Luster
- Dull or submetallic
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Black, dark gray, or reddish-brown; Luster: Dull or submetallic; Structure: Highly vesicular (full of holes); Cleavage: None; Specific Gravity: Low (1.2 - 2.0).
Formation & geological history
Formed from gas-rich basaltic or andesitic magma. As the magma is ejected during a volcanic eruption, dissolved gases expand quickly, creating a frothy texture that solidifies as the rock cools rapidly on the surface.
Uses & applications
Used in landscaping for ground cover, as a drainage material in civil engineering, in gas grills for heat retention, as an abrasive agent, and occasionally in lightweight concrete or road construction.
Geological facts
Scoria is often confused with pumice, but it is denser and has larger vesicles with thicker walls. Unlike pumice, most scoria specimens will sink in water due to their higher iron and magnesium content.
Field identification & locations
Identify by its dark color, porous 'honeycomb' texture, and relatively light weight despite being stony. Commonly found near cinder cones and volcanic vents in regions like Hawaii, Iceland, and the American Southwest.
