igneous
Likely weathered basalt (vesicular/amygdaloidal basalt)
Basalt; chiefly plagioclase feldspar, clinopyroxene, and iron-magnesium minerals, possibly with olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to weakly subvitreous surface with lighter weathering patches; typically hardness 5–6, no obvious cleavage, and specific gravity about 2.8–3.1. The image does not show diagnostic vesicles or crystals clearly enough for certainty.
Identified More igneous →
Explore Likely weathered basalt (vesicular/amygdaloidal basalt) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-brown, fine-grained, dull to weakly subvitreous surface with lighter weathering patches; typically hardness 5–6, no obvious cleavage, and specific gravity about 2.8–3.1. The image does not show diagnostic vesicles or crystals clearly enough for certainty.
Formation & geological history
An extrusive igneous rock formed when basaltic lava cooled rapidly at or near Earth’s surface, commonly from volcanic flows, seafloor spreading, or hotspots. Its exact age and locality cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, road stone, riprap, and construction material; attractive polished pieces may be sold as decor or teaching specimens. This ordinary fragment has minimal commercial value.
Geological facts
Basalt is the most widespread volcanic rock and forms much of the oceanic crust. Brown coloration commonly reflects surface weathering and oxidation of iron-bearing minerals.
Field identification & locations
Identify by its dense dark color, fine texture, heavy feel, and lack of visible layered structure; a streak, magnetism test, and fresh broken surface would help distinguish it from andesite or weathered gabbro. Common worldwide, especially volcanic regions and river gravels.
