igneous
Weathered basaltic rock fragment
Basalt, likely porphyritic or amygdaloidal basalt with weathered iron-oxide-rich zones
AI-generated identification · may be incorrectDark gray-black, fine-grained, dull to weakly subvitreous luster, with reddish-brown weathering and pale granular veins or inclusions. Typical basalt hardness is about 6 Mohs, specific gravity 2.8–3.0, and it has no obvious cleavage; visible crystals may include plagioclase and pyroxene.
Identified More igneous →
Explore Weathered basaltic rock fragment in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-black, fine-grained, dull to weakly subvitreous luster, with reddish-brown weathering and pale granular veins or inclusions. Typical basalt hardness is about 6 Mohs, specific gravity 2.8–3.0, and it has no obvious cleavage; visible crystals may include plagioclase and pyroxene.
Formation & geological history
An extrusive igneous rock formed when mafic lava cooled rapidly at or near Earth’s surface, generally in the Cenozoic or older volcanic terrains. The rusty coloration reflects oxidation and surface weathering; exact identification would require a fresh surface or laboratory testing.
Uses & applications
Commonly used as crushed aggregate, road stone, riprap, and building stone; attractive polished pieces may be used decoratively. This small weathered fragment has little commercial value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of the oceanic crust. Pale material may represent plagioclase-rich veins, weathered alteration minerals, or an attached felsic fragment.
Field identification & locations
Identify it by its heavy feel, dark fine-grained matrix, hardness, and lack of visible layering; it commonly occurs in lava flows, volcanic fields, and river gravels. A streak, acid test, magnet test, and thin section would help distinguish it from slag or other dark rocks.
