sedimentary

Black Sand (Magnetite Sand)

Magnetite-rich Placers (Fe3O4)

AI-generated identification · may be incorrect

Hardness: 5.5-6.5 (for magnetite grains); Color: Black, dark grey, peppered with white/tan; Luster: Metallic to submetallic; Crystal Structure: Isometric (grains are often worn octahedrons); Specific Gravity: 5.17-5.18.

Hardness: 5
Color: Black, dark grey, peppered with white/tan
Luster: Metallic to submetallic

Identified May 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the erosion and weathering of mafic igneous or metamorphic rocks. Heavy minerals like magnetite are concentrated by water or wind action into placer deposits in rivers or coastal shorelines.

Uses & applications

Used as an ore for iron, in heavy media separation, as an abrasive agent, for landscape design, and in experimental gold prospecting kits.

Geological facts

Magnetite is the most magnetic mineral on Earth. In some locations, black sand beaches are formed from basaltic volcanic rock, while inland deposits are often associated with ancient riverbeds.

Field identification & locations

Identified by its dark color and attraction to a magnet. Commonly found on beaches near volcanic areas or in river deltas. You can test it by running a magnet over the grains; the magnetite will jump to the magnet.