metamorphic
Magnetite-rich iron ore (probable magnetite schist)
Magnetite (Fe₃O₄) in a foliated metamorphic matrix, possibly magnetite–biotite schist
AI-generated identification · may be incorrectBlack to steel-gray, strongly metallic to submetallic luster, uneven fractured surface, and likely high density (specific gravity about 5.2 for magnetite). Magnetite is Mohs 5.5–6.5, commonly granular rather than visibly crystalline, and strongly magnetic;…
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Physical properties
Black to steel-gray, strongly metallic to submetallic luster, uneven fractured surface, and likely high density (specific gravity about 5.2 for magnetite). Magnetite is Mohs 5.5–6.5, commonly granular rather than visibly crystalline, and strongly magnetic; the specimen appears foliated and sparkly from mica or sulfides.
Formation & geological history
Likely formed when iron-rich sediments or volcanic material underwent regional metamorphism and recrystallization; the exact geological age cannot be determined from the photograph. Similar ores occur in Precambrian banded iron formations and metamorphosed iron deposits.
Uses & applications
Used as iron ore, dense aggregate, pigment, and a source of magnetic material; attractive pieces are collected but are generally not gemstone grade.
Geological facts
A hand magnet should attract it strongly, and its black streak distinguishes magnetite from many shiny sulfide minerals. Weathering commonly produces reddish-brown hematite or limonite coatings.
Field identification & locations
Common in metamorphic terrains and iron-ore districts worldwide, especially Michigan, Minnesota, Sweden, Brazil, India, and Australia. Confirm with magnetism, streak testing, density, and ideally chemical analysis; pyrite or hematite may be associated.
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