What Is Spinel? The Gem Mistaken for Ruby in the Crown Jewels

Spinel is a magnesium aluminum oxide mineral, and for most of human history, gemologists had no reliable way to distinguish fine red spinel from ruby (a variety of corundum) — the two can occur in a strikingly similar vivid red, and it wasn't until the 20th century, with the development of modern gemological testing, that the distinction could be made with certainty.

Mistaken Identity in the Crown Jewels

The Black Prince's Ruby, set in the British Imperial State Crown and with a documented history reaching back to 14th-century Spain, is actually a large red spinel, not a ruby — a fact only confirmed relatively recently in gemological terms. Similar cases exist in other royal and historical collections, meaning spinel has quietly played a starring role in some of history's most famous "ruby" jewelry for centuries without anyone knowing.

A Wide Color Range

Beyond red, spinel occurs naturally in pink, orange, purple, blue and a vivid, saturated pinkish-red sometimes called "flame spinel" — one of the wider natural color ranges among gem minerals, generally without the routine heat treatment common to many other colored stones, since spinel's natural color is often already vivid and stable.

Why It's Historically Underappreciated

Because spinel lacks the centuries of dedicated marketing and cultural mythology built up around "traditional" gems like ruby, sapphire and emerald, fine natural spinel has historically sold for a fraction of what visually comparable rubies command — genuinely a case where rarity and beauty don't track price, largely for market-history reasons rather than any real difference in desirability once the stone is properly identified.

Where It's Mined

Myanmar (Burma) is the historic and continuing source of the finest red spinel, often found in the same gem gravels as Burmese ruby. Sri Lanka, Tanzania and Tajikistan are other significant sources.

Quick Facts

Composition: magnesium aluminum oxide — Hardness: 7.5–8 on the Mohs scale — Historically confused with ruby (including in the British Crown Jewels) — Wide natural color range, rarely treated — Major source: Myanmar.