igneous
Basalt with Pahoehoe flow texture
Vesicular Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0. Features ropey 'pahoehoe' surface texture.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0. Features ropey 'pahoehoe' surface texture.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium and iron-rich lava. The ropey surface texture indicates a 'Pahoehoe' flow, where the cooling skin is wrinkled by movement of liquid lava beneath. Usually Cenozoic to Holocene in age for surface-preserved textures.
Uses & applications
Used primarily in construction as crushed stone, aggregate for asphalt, and historically for stone tools. Specimens with distinct flow textures are valued for educational and geological collections.
Geological facts
Pahoehoe is a Hawaiian term. It is the most common rock type on Earth's surface when including the ocean floor. The surface texture can tell geologists the exact direction the lava was flowing millions of years ago.
Field identification & locations
Identify by its dark color, high density, and the presence of small holes (vesicles) or ropey ridges on the surface. Found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest (Columbia River Basalts).
