Magnetite

Magnetite is an oxide of iron. When you see sparks from welding operations or from iron striking a hard surface, rapid oxidation of iron particles turns it into Magnetite. Magnetite is a natural magnet that was first discovered by a Greek sheapard nmed Magnes who saw his shoe nails stuck to a rock containing magnetite.

•Color is black.
•Luster is metallic to dull.
•Transparency: Crystals are opaque.
•Crystal System is isometric; 4/m bar 3 2/m
•Crystal Habits are typically octahedrons but rarely rhombododecahedron and other isometric forms, most commonly found massive or granular. Twinning of octahedrons into spinel law twins is seen occasionally.
•Cleavage is absent although octahedral parting can be seen on some specimens.
•Fracture is conchoidal.
•Hardness is 5.5 - 6.5
•Specific Gravity is 5.1+ (average for metallic minerals)
•Streak is black.
•Associated Minerals are talc and chlorite (schists), pyrite and hematite.
•Other Characteristics: Magnetism stronger in massive examples than in crystals, striations on crystal faces (not always seen).
•Notable Occurrences include South Africa, Germany, Russia and many localities in the USA.
•Best Field Indicators are magnetism, crystal habit and streak.

Reference:http://www.galleries.com/Magnetite