igneous
Weathered metal-rich igneous rock, likely basalt or komatiitic peridotite
Probable altered mafic–ultramafic rock containing pyroxene/amphibole, olivine, iron oxides, and possible metallic sulfides
AI-generated identification · may be incorrectDark gray to olive-brown, fine- to medium-grained, locally shiny, with a dense massive texture and irregular fracture; estimated Mohs hardness 5–7 and specific gravity about 2.9–3.5. The reflective grains may be magnetite, pyrite, or weathered sulfides rather than native metal.
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Physical properties
Dark gray to olive-brown, fine- to medium-grained, locally shiny, with a dense massive texture and irregular fracture; estimated Mohs hardness 5–7 and specific gravity about 2.9–3.5. The reflective grains may be magnetite, pyrite, or weathered sulfides rather than native metal.
Formation & geological history
Likely formed from rapidly cooled mafic lava or a shallow ultramafic intrusion, then chemically altered and oxidized near the surface; age cannot be determined from the photograph. Brown coloration suggests weathering of iron-bearing minerals.
Uses & applications
Typically used as aggregate, road stone, or a geological teaching/collecting specimen; it has little gem value unless confirmed to contain attractive sulfides or unusual minerals.
Geological facts
Mafic rocks commonly contain abundant iron and magnesium and may be weakly to strongly magnetic if magnetite-rich. A streak, magnet test, hardness test, and fresh broken surface would substantially improve identification.
Field identification & locations
Common in volcanic and ophiolite terrains, including oceanic crust exposures and ancient greenstone belts. Check whether it attracts a magnet, leaves a dark streak, or shows brassy sulfide crystals; avoid assuming the shiny areas are gold.
