mineral

Black Spinel

Magnesium Aluminum Oxide (MgAl2O4)

Hardness: 8 on Mohs scale; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Isometric (cubic/octahedral); Cleavage: Indistinct; Specific Gravity: 3.54-3.63

Hardness: 8 on Mohs scale
Color: Jet black
Luster: Vitreous (glassy)

Identified April 29, 2026More mineral →

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Physical properties

Hardness: 8 on Mohs scale; Color: Jet black; Luster: Vitreous (glassy); Crystal Structure: Isometric (cubic/octahedral); Cleavage: Indistinct; Specific Gravity: 3.54-3.63

Formation & geological history

Formed primarily as a metamorphic mineral in limestone or as a primary mineral in mafic igneous rocks. It is also common in alluvial deposits after weathering out of harder matrix rocks.

Uses & applications

Used almost exclusively in the jewelry industry as a durable and affordable alternative to black diamonds or black sapphires. It is highly valued for its high refractive index and deep black color.

Geological facts

Black Spinel was often mistaken for black diamond or tourmaline in antiquity. It is one of the hardest minerals and is remarkably stable under high heat and chemical exposure. Famous red 'rubies' in royal crowns are often actually Spinels.

Field identification & locations

Identified in the field by its distinct octahedral crystal habit when found in matrix, and its extreme hardness which prevents scratching by steel. Common locations include Thailand, Sri Lanka, and Myanmar.