mineral
Polished magnetite-rich ironstone (possible magnetite pebble)
Magnetite, Fe₃O₄; possibly magnetite-bearing basalt or ironstone
AI-generated identification · may be incorrectBlack to dark gray, opaque, metallic-to-submetallic luster, commonly fine-grained and rounded from tumbling; Mohs hardness about 5.5–6.5, relatively dense (specific gravity ~5.2 for pure magnetite), and strongly magnetic. The image alone cannot confirm whether it is pure magnetite or a magnetite-rich rock.
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Physical properties
Black to dark gray, opaque, metallic-to-submetallic luster, commonly fine-grained and rounded from tumbling; Mohs hardness about 5.5–6.5, relatively dense (specific gravity ~5.2 for pure magnetite), and strongly magnetic. The image alone cannot confirm whether it is pure magnetite or a magnetite-rich rock.
Formation & geological history
Magnetite forms in igneous and metamorphic environments, hydrothermal veins, and sedimentary iron deposits; basaltic source rocks may be hundreds of millions to billions of years old. The smooth shape and shine indicate natural water wear or human polishing.
Uses & applications
Used as iron ore, pigment, dense media, and for magnetic materials; attractive polished pieces are collected but are generally not jewelry gemstones.
Geological facts
Magnetite is one of the most strongly magnetic common minerals and can form naturally magnetized lodestone. Its black streak distinguishes it from many dark silicate rocks.
Field identification & locations
Test with a strong magnet and check for a black streak on unglazed ceramic; unusually high heft supports magnetite. Common sources include iron-ore regions, volcanic terrains, and black-sand beaches.
