Spinel was recognized as an individual mineral only 150 years ago.Before then it was classed as ruby.
It occurs in all colors , the favorite being a ruby-like red.
The Moh’s hardness is 8.
Large stones are rare and star spinels are very rare.
Some well-known “rubies” are really spinels , such as the “Black Prince’s Ruby” in the English Crown and the 361 ct “Timur Ruby” in a necklace in the English Crown Jewels.The drop-shaped spinels in the Wittelsbach crown of 1830 were also originally thought to be rubies.
Spinel occurs with ruby and sapphire in placer deposits , mainly in Burma (Myanmar,near Mogok),Sri Lanka(near Ratnapura).Other important deposits are found in Madagascar and Tanzania.
The two largest spinels found are formed as roundish octaedrons weigh 520ct each exposed at the British Museum of London.