igneous
Iron-rich volcanic rock, possibly hematite-bearing basalt
Basalt with iron oxides/hydroxides, chiefly hematite (Fe₂O₃) and possibly magnetite (Fe₃O₄)
AI-generated identification · may be incorrectDark maroon to black, dull-to-submetallic luster, fine-grained and massive with irregular fractures; likely Mohs 5–6, with moderate-to-high density. Pale metallic patches may be iron minerals or weathering products; image alone cannot confirm exact identification.
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Physical properties
Dark maroon to black, dull-to-submetallic luster, fine-grained and massive with irregular fractures; likely Mohs 5–6, with moderate-to-high density. Pale metallic patches may be iron minerals or weathering products; image alone cannot confirm exact identification.
Formation & geological history
Likely formed from rapidly cooled mafic lava, later altered and oxidized near the surface; commonly Precambrian to recent, depending on locality.
Uses & applications
Common basalt is used as aggregate, road stone, and construction material; attractive iron-rich pieces are collected but generally have little gem value.
Geological facts
Hematite produces red-brown streak and is nonmagnetic; magnetite produces a black streak and may attract a magnet. A streak test and magnet test would substantially improve identification.
Field identification & locations
Common in volcanic terrains and iron-rich weathering zones worldwide. Check for vesicles, a reddish-brown streak, magnetism, and hardness sufficient to scratch glass; metallic yellow flecks could also indicate pyrite or chalcopyrite.
