igneous
Likely weathered basalt or iron-rich volcanic rock
Basalt; primarily plagioclase feldspar, pyroxene, and possibly olivine with iron-oxide alteration
AI-generated identification · may be incorrectDark brown-black, fine-grained, dull to weakly vitreous luster, and irregular massive texture; estimated Mohs hardness 5–6, with no obvious cleavage. The reddish-brown areas likely reflect oxidation of iron-bearing minerals.
Identified More igneous →
Explore Likely weathered basalt or iron-rich volcanic rock in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark brown-black, fine-grained, dull to weakly vitreous luster, and irregular massive texture; estimated Mohs hardness 5–6, with no obvious cleavage. The reddish-brown areas likely reflect oxidation of iron-bearing minerals.
Formation & geological history
Basalt forms when mafic lava rapidly cools at or near Earth’s surface, commonly in volcanic fields and oceanic crust. Its exact age cannot be determined from the photograph and may range from recent to billions of years.
Uses & applications
Used widely as crushed aggregate, road material, riprap, and building stone; small attractive pieces are occasionally collected. This specimen has little commercial value unless it proves to be an unusual mineral or meteorite.
Geological facts
Basalt is the most common volcanic rock on Earth and commonly develops a dark, fine-grained appearance. A more precise identification requires a fresh surface, streak, density, and mineral examination.
Field identification & locations
Commonly found in volcanic regions, river gravels, and landscaping stone. It is not possible to distinguish basalt confidently from slag, chert, or a meteorite by image alone; test for magnetism, streak, bubbles, and unusually high density.
