igneous
Basalt Pebble
Extrusive mafic igneous rock
Hardness 6 on the Mohs scale, dark gray to brownish-black color, dull to sub-vitreous luster when wet or river-polished, fine-grained (aphanitic) texture, high specific gravity (~2.8 - 3.0)
Identified More igneous →
Explore Basalt Pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness 6 on the Mohs scale, dark gray to brownish-black color, dull to sub-vitreous luster when wet or river-polished, fine-grained (aphanitic) texture, high specific gravity (~2.8 - 3.0)
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Stream or beach erosion smooths and rounds the rock over long periods into a river pebble.
Uses & applications
Commonly used as decorative river stone, landscaping, aggregate for construction, and as tumbling specimens for rock collectors.
Geological facts
Basalt makes up over 90 percent of all volcanic rock on Earth and forms the majority of the oceanic crust as well as vast flood basalt plateaus on land.
Field identification & locations
Look for a dark, heavy, fine-grained pebble with rounded edges resulting from water erosion. Frequently found along riverbeds, beaches, and glacial gravel deposits globally.
