Magnetite

Hardness: 5-6 (Mohs scale); Color: Typically dark gray to black, often with a metallic sheen; Luster: Metallic to submetallic; Crystal Structure: Isometric (cubic) - often forms octahedral or dodecahedral crystals, though massive or granular aggregates are common; Cleavage: None; Specific Gravity: 4.8 - 5.3

Magnetite crystals form in a variety of igneous, metamorphic, and sedimentary environments. In igneous rocks, it crystallizes from cooling magma as an accessory mineral or in larger segregated bodies. In metamorphic rocks, it forms during regional or contact metamorphism of iron-rich sediments. In sedimentary environments, it can form as a detrital mineral in placers due to its high density and resistance to weathering, or through chemical precipitation. Geological age varies widely depending on the specific formation.

Magnetite is a primary iron ore, crucial for steel production. It is used as a heavy aggregate in concrete for radiation shielding and as a ballast. In some niche applications, it is used as a pigment, as a medium in dense media separation, and in magnetic recording tapes. Historically, lodestone (naturally magnetized magnetite) was used in compasses.

Magnetite is the most magnetic of all naturally occurring minerals on Earth. Its strong magnetism has been known since ancient times and was used in the first compasses. It can sometimes be found as lodestone, which is naturally magnetized magnetite. Magnetite is an important iron ore, and its presence can sometimes be detected by simply using a magnet.

To identify magnetite in the field, its strong magnetism is the most definitive characteristic; a hand magnet will easily pick up small pieces or be attracted to larger specimens. Its dark color, metallic luster, and high density are also good indicators. It is commonly found in igneous rocks (like gabbro, basalt, peridotite), metamorphic rocks (like banded iron formations, skarns), and placer deposits. Collectors often seek well-formed octahedral crystals. Look for it in areas with iron ore deposits or in stream beds where heavy minerals accumulate.