mineral

Black Diamond / Black Sapphire

Carbon (C) or Corundum (Al2O3)

Hardness: 9.0 (Sapphire) to 10.0 (Diamond). Color: Opaque black or deep dark blue. Luster: Adamantine to vitreous. Crystal structure: Isometric (Diamond) or Trigonal (Sapphire). Specific gravity: 3.5-4.0.

Hardness: 9
Color: Opaque black or deep dark blue
Luster: Adamantine to vitreous

Identified April 4, 2026More mineral →

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Physical properties

Formation & geological history

Diamonds form under high pressure/temperature in the Earth's mantle and are brought up by kimberlite eruptions. Sapphires form in metamorphic and igneous rocks like marble or basalt.

Uses & applications

Primary use is in fine jewelry as center stones or accents. Industrial-grade varieties are used as abrasives or for cutting tools due to extreme hardness.

Geological facts

Natural black diamonds, also known as Carbonado, are believed by some researchers to have originated from interstellar space via meteorites. Black sapphires are often less expensive than blue ones but are prized for their sleek, modern look.

Field identification & locations

Identify in jewelry settings by checking for natural inclusions or surface scratches. Use a hardness tester or thermal conductivity probe for confirmation. Commonly found in mines in Brazil, Central Africa, Australia, and Thailand.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

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Epidote

Epidote - Ca2(Al2,Fe3+)3(SiO4)3(OH)

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