Spinel: the great imitator that fooled royalty

Spinel is a genuinely underrated gemstone that comes in a wide color range including a red that has historically been confused with ruby, most famously several stones in European crown jewels long believed to be rubies were only identified as red spinel through modern gemological testing, well after they were already famous historical gems. Hardness runs about 8, durable and well suited to jewelry. Spinel forms in the same general metamorphic and skarn environments as ruby, which is part of why the two have historically been found and worn together without anyone realizing they were different minerals until proper testing became available.