Historically often confused with corundum (rubies and sapphires), spinel is
chemically different, although its appearance and colours are similar. The central
stone in England’s state crown is, in fact, spinel, although at the time it was set it
was thought to have been a ruby. Distinct in both composition (hard vitreous
magnesium aluminium oxide) and structure (octahedral crystals), these days
spinel is acknowledged as a precious stone in its own right.