Ferrous-Ferric Oxide Fe3O4
Magnetite is strongly magnetic. It was used by the ancient Chinese to make the first magnetic compasses.
Magnetite reacts with oxygen to produce hematite, another iron ore.
In crystalline form magnetite is usually octahedral. It has a hardness of 5.5 - 6.5 on the Mohs Scale. It is black with a black streak and has a metallic luster.
The occurrence of magnetite is widespread. It is commonly found in igneous, and metamorphic rocks. Some sedimentary rocks have magnetite present in them as well. Large deposits are found in Kiruna, Sweden, the Adirondack area in New York, and the Pilbara region of Western Australia. Lesser deposits are found in Europe, North and South America, and Africa.
Because of its magnetic signature magnetite is used by scientists in understanding plate techtonics.
Chemical formula: Ferrous-Ferric Oxide Fe3O4
Luster: metallic, greasy, dull
Crystal system: cubic
Specific Gravity: 5.2
Hardness (Mohs): 5.5
Uses: iron ore
Location: Kiruna, Sweden, the Adirondack area in New York, and the Pilbara region of Western Australia