Spinel
Spinel is one of history's most misunderstood gems — many of history's most famous "rubies" are actually spinels. The Black Prince's Ruby in the British Crown Jewels is actually a 170-carat red spinel. Spinel forms in the same metamorphic environments as ruby (marble) and has very similar color and properties. It was officially added as an August birthstone in 2016. Montana and Sri Lanka produce fine gem-quality material.
Physical Properties
Chemical Formula
MgAl₂O₄
Hardness (Mohs)
7.5–8
Color
Red, pink, orange, blue, black, colorless — all colors
Luster
Vitreous to subadamantine
Crystal System
Cubic (isometric)
Streak
White
Cleavage
Imperfect octahedral
Specific Gravity
3.54–3.99
🔍 Field Identification Tips
Octahedral crystal habit (8 faces — like two pyramids joined at the base) is distinctive. Hardness 7.5–8. Vitreous luster. No cleavage (very tough). Distinguished from ruby by isometric crystal system (ruby is hexagonal), lack of silk (rutile inclusions), and different fluorescence pattern under UV. Spinel is singly refractive; ruby is doubly refractive.
Varieties & Forms
📍 Where to Find Spinel in the US
Uses & Applications
Fine jewelry (August birthstone since 2016), collectors specimens. Has been confused with ruby throughout history.
💰 Collector Value Guide
Common black spinel: $5–$50. Red/pink faceted: $50–$500/ct. Fine unheated red: $500–$5,000/ct. Top Burmese red spinel: $10,000+/ct.
Find Spinel With Our Tools
Use the We Lick Rocks app to identify specimens, find dig sites, and connect with local rockhounds.