mineral
Raw Corundum (Sapphire/Ruby variant)
Aluminum oxide (Al2O3)
Hardness: 9 on Mohs scale; Color: Grayish-purple to blue; Luster: Adamantine to vitreous; Crystal structure: Trigonal/Hexagonal barrel shapes; Specific gravity: 3.95-4.10
- Hardness
- 9 on Mohs scale
- Color
- Grayish-purple to blue
- Luster
- Adamantine to vitreous
Identified More mineral →
Explore Raw Corundum (Sapphire/Ruby variant) in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 9 on Mohs scale; Color: Grayish-purple to blue; Luster: Adamantine to vitreous; Crystal structure: Trigonal/Hexagonal barrel shapes; Specific gravity: 3.95-4.10
Formation & geological history
Formed in silica-poor igneous rocks (syenites, pegmatites) or metamorphic rocks like mica schists and crystalline limestones. Crystallizes at high temperature and pressure.
Uses & applications
Industrial abrasives, watch bearings, and gemstones. Non-gem quality specimens like this are primarily for mineral collection or industrial use.
Geological facts
Corundum is the second hardest natural mineral after diamond. A variety called 'emery' is a mixture of corundum and other minerals used for sandpaper.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by steel or quartz) and characteristic hexagonal barrel-shaped crystal habit. Often found in alluvial deposits due to high density.
More like this
Other mineral specimens
Sandstone (with potential mineral staining/concretions)
Arenite (SiO2 based)
sedimentary
Schist
Schist
Metamorphic
Epidote
Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)
metamorphic
Gypsum (variety Selenite or Alabaster)
Calcium sulfate dihydrate (CaSO4·2H2O)
Mineral
Nephrite Jade
Nephrite
Mineral/Rock
Banded Gneiss (River Rock/Pebble)
Gneiss (specifically a banded variety often found as a river rock)
Metamorphic Rock