What are Balas Rubies and Ruby Spinels?

Rubies are Red, Sapphires are Blue, Spinels are Both

Spinels are beautiful, durable gemstones that occur in various colors, including deep reds that rival rubies and cobalt blues that rival sapphires. Unfortunately, that rivalry with corundum — the mineral species that includes rubies and sapphires — hasn’t always favored spinel. For centuries, red spinel was considered a type of ruby: a “balas ruby.”

How Does Modern Gemology Distinguish Ruby and Spinel?

Gemologists now distinguish spinel and corundum as distinct gem species. Chemical formulas and crystal structure define gem species. Corundum, for example, has a chemical formula of Al₂O₃ and a hexagonal crystal structure. Ruby is the red variety of corundum, and the presence of chromium impurities creates its red color. All other varieties of corundum are called sapphires, with various impurities creating other colors like blue, purple, and pink. Colorless corundum, without impurities, is considered white sapphire.

Spinel has a chemical formula of MgAl₂O₄ and an isometric crystal structure. Various impurities