igneous
Pahoehoe Basalt
Extrusive mafic volcanic rock
Hardness: 5-6 Mohs. Color: Charcoal gray to black, weathering to reddish-brown. Luster: Dull to sub-metallic. Structure: Vesicular with a ropy, billowy, or swirled surface texture. Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Charcoal gray to black, weathering to reddish-brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Charcoal gray to black, weathering to reddish-brown. Luster: Dull to sub-metallic. Structure: Vesicular with a ropy, billowy, or swirled surface texture. Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, gas-rich basaltic lava. The 'ropy' texture occurs as the molten interior continues to flow beneath a cooling, plastic skin. They are typically found in active volcanic hotspots like Hawaii or Iceland.
Uses & applications
Used primarily in construction as crushed stone, road base, or concrete aggregate. In landscaping, it is used for decorative rock or lava rock grills. Occasionally used as a study specimen for vulcanology.
Geological facts
Pahoehoe is a Hawaiian word meaning 'smooth, unbroken lava'. It is one of the two main types of subaerial lava flows, the other being 'A'a. The surface can often form 'lava toes' or small lobes as the flow advances.
Field identification & locations
Identify in the field by its distinct ropy or rippled surface that looks like twisted rope. It is much smoother to walk on than 'A'a lava. Common in the Hawaiian Islands, Galápagos, and Craters of the Moon, Idaho.
