Raw Corundum (Sapphire/Ruby variant)

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.

Identified on: 5/19/2026

Mode: Standard