mineral
Tumbled magnetite-rich rock
Magnetite (Fe₃O₄), likely in a mafic-rock matrix
AI-generated identification · may be incorrectBlack to brown-black, opaque, metallic to submetallic luster; Mohs hardness 5.5–6.5, irregular fracture, no obvious cleavage, and typically strong magnetism. The rounded shape and glossy surface indicate tumbling or water wear.
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Physical properties
Black to brown-black, opaque, metallic to submetallic luster; Mohs hardness 5.5–6.5, irregular fracture, no obvious cleavage, and typically strong magnetism. The rounded shape and glossy surface indicate tumbling or water wear.
Formation & geological history
Magnetite crystallizes in igneous and metamorphic environments and accumulates in placer deposits; Earth specimens commonly range from Precambrian to modern. The exact matrix and locality cannot be determined from the photograph.
Uses & applications
Used as an iron ore, dense aggregate, pigment, and industrial magnetic material; attractive polished pieces are sold as curiosities and teaching specimens.
Geological facts
Magnetite is the most magnetic common mineral and can form naturally magnetized lodestone. Its dark appearance may also overlap with hematite, basalt, or slag, so a magnet test is useful.
Field identification & locations
Check for strong attraction to a magnet, black streak, and high density; magnetite leaves a black streak, whereas hematite commonly gives a red-brown streak. Common sources include Sweden, Russia, South Africa, the United States, and New Zealand.
