mineral

Ruby (Raw Corundum)

Corundum (Al2O3 with Chromium impurities)

Hardness: 9 on Mohs scale; Color: Pinkish-red to deep red; Luster: Adamantine to vitreous; Crystal Structure: Hexagonal/Trigonal (often found as flat hexagonal plates); Cleavage: None (has parting); Specific Gravity: 3.97-4.05.

Hardness: 9 on Mohs scale
Color: Pinkish-red to deep red
Luster: Adamantine to vitreous

Identified June 22, 2026More mineral →

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Physical properties

Formation & geological history

Formed in aluminum-rich metamorphic rocks such as marble or schist, and in igneous environments like syenites. They are found in deposits ranging from Precambrian to more recent alluvial gravels.

Uses & applications

Used primarily as a gemstone in jewelry. Industrial uses include lasers, watches (bearings), and high-durability optical windows.

Geological facts

Ruby is the red variety of Corundum; any other color is called Sapphire. It is the second hardest natural material after diamond. Its red color is caused specifically by the presence of chromium.

Field identification & locations

Identify in the field by its distinct hexagonal crystal habit and its extreme hardness (will scratch almost any other mineral). Common locations include Myanmar, Sri Lanka, Thailand, and Madagascar.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

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)]

mineral