The Spinel/Ruby confusion
Spinel comes in many colors including red,
pink,
blue and purple. It was not until 1973 that the gemstone Spinel was recognized as a mineral distinct from corundum (ruby and
sapphire). Spinel is magnesium oxide while corundum is aluminium oxide. Many famous gemstones in crown jewels around the world were thought to be
rubies but are actually Spinel. The most famous is the Black Prince