Magnetite

Hardness (Mohs scale): 6-7, Color: Typically dark gray to black with a metallic to submetallic luster, though can exhibit iridescent tarnishes. Streak is black. Crystal Structure: Isometric (cubic) - often forms octahedral or dodecahedral crystals, but can also be granular or massive.

Magnetite is an accessory mineral in many igneous and metamorphic rocks and is common in black sands. It forms under a wide range of geological conditions, including direct crystallization from magma, hydrothermal alteration, and metamorphism of iron-rich sediments. It is present in rocks of all geological ages.

Primarily used as a major ore of iron (steel production). Due to its magnetic properties, it's used in various applications like magnetic pigments, heavy media separation, and as a raw material for ferrites used in electronics. Finely ground magnetite is also used in the coal industry for coal washing.

Magnetite is one of the most common iron oxides and is highly magnetic. It is the mineral with the highest iron content (72.4%) by weight, making it a primary iron ore. Naturally occurring magnetite can be found in some living organisms, such as magnetotactic bacteria, which use it to orient themselves to the Earth's magnetic field.

In the field, magnetite can be identified by its strong magnetism (it will attract a common magnet). Its dark color and metallic luster are also good indicators. It often occurs as disseminated grains or massive aggregates in igneous and metamorphic rocks, and can be concentrated in placer deposits. Common locations include iron ore deposits globally (e.g., Sweden, Russia, USA, Brazil), and as black sands on beaches derived from the weathering of mafic igneous rocks.