mineral

Magnetite / Ironstone

Magnetite (Fe3O4)

Hardness: 5.5-6.5 Mohs; Color: Iron-black to dark grey with rusty highlights; Luster: Metallic to sub-metallic; Crystal structure: Isometric; Cleavage: None; Specific gravity: 5.1-5.2 (very heavy).

Hardness: 5
Color: Iron-black to dark grey with rusty highlights
Luster: Metallic to sub-metallic

Identified April 12, 2026More mineral →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 5.5-6.5 Mohs; Color: Iron-black to dark grey with rusty highlights; Luster: Metallic to sub-metallic; Crystal structure: Isometric; Cleavage: None; Specific gravity: 5.1-5.2 (very heavy).

Formation & geological history

Formed in igneous, metamorphic, and sedimentary environments. Often found as 'black sand' in placer deposits due to its high density and resistance to weathering. These specimens typically form in high-temperature environments or via hydrothermal precipitation.

Uses & applications

Primary ore of iron. Used in industrial processes as a heavy media for coal separation, in construction as high-density concrete aggregate, and in scientific research regarding paleomagnetism.

Geological facts

Magnetite is the most magnetic of all the naturally occurring minerals on Earth. Pieces of magnetite that are naturally magnetized are called lodestones and were used in the first compasses in history.

Field identification & locations

Identify in the field by its high density (feels heavy for its size) and strong attraction to a magnet. Look for a black streak when rubbed on a porcelain plate. Common in river beds and mining tailings.