mineral

Magnetite / Ironstone

Magnetite (Fe3O4)

Hardness: 5.5-6.5 Mohs; Color: Black to dark gray; Luster: Metallic to sub-metallic; Crystal Structure: Isometric; Cleavage: None (parting); Specific Gravity: 5.1-5.2; Strongly magnetic.

Hardness: 5
Color: Black to dark gray
Luster: Metallic to sub-metallic

Identified July 7, 2026More mineral →

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Physical properties

Hardness: 5.5-6.5 Mohs; Color: Black to dark gray; Luster: Metallic to sub-metallic; Crystal Structure: Isometric; Cleavage: None (parting); Specific Gravity: 5.1-5.2; Strongly magnetic.

Formation & geological history

Formed in igneous, metamorphic, and sedimentary environments. Often occurs as a primary mineral in mafic igneous rocks or through contact metamorphism. Can also concentrate as 'black sand' in sedimentary deposits.

Uses & applications

Major ore of iron; used in heavy media separation, as a pigment (mars black), and for its magnetic properties in industrial applications.

Geological facts

Magnetite is the most magnetic of all the naturally-occurring minerals on Earth. Naturally magnetized pieces called lodestones were used by ancient mariners as the first compasses.

Field identification & locations

Identify in the field by its black streak on a porcelain plate, its heavy weight (high density), and its strong attraction to a magnet. Commonly found in massive forms or as octahedral crystals.