igneous
Basalt (Volcanic Peak)
Extrusive Mafic Igneous Rock
Hardness: 6–7 Mohs. Color: dark gray, black, or reddish-brown When weathered. Luster: dull to earthy. Structure: fine-grained (aphanitic) or porphyritic. Cleavage: none.
- Hardness
- 6–7 Mohs
- Color
- dark gray, black, or reddish-brown When weathered
- Luster
- dull to earthy
Identified More igneous →
Explore Basalt (Volcanic Peak) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6–7 Mohs. Color: dark gray, black, or reddish-brown When weathered. Luster: dull to earthy. Structure: fine-grained (aphanitic) or porphyritic. Cleavage: none.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface. These specific peaks in Hawaii (likely Kauai) are remnants of shield volcanoes from the Pliocene epoch, approximately 4-5 million years ago.
Uses & applications
Used in construction as crushed stone for road bases and concrete aggregate. In landscaping, it is used for decorative walls and rockeries.
Geological facts
The peak shown is part of a heavily eroded volcanic caldera remnant. Basalt is the most common rock type in the Earth's crust and also makes up the majority of the ocean floors.
Field identification & locations
Identified by its dark color, heavy weight (high specific gravity), and fine-grained texture. Commonly found in volcanic island chains like Hawaii and Iceland.
