Spinel

A durable (H=8) magnesium aluminum oxide (MgAl₂O₄) whose impurities impart colour: blue (cobalt), red (chromium); purple (iron-zinc-chromium), & black (iron±titanium). Formed in magnesium-rich metamorphic rocks such as marbles, often with corundum.

Main Photo Credit: "Spinel" by NRCan, 2026. Used with permission.