Spinel is most famous for its deep red variety that closely resembles Ruby. These two gemstones can be very difficult to distinguish. Until the late 19th century, there was no distinction made between Ruby and red Spinel, as they look identical and are found in the same localities. Many famous old “Rubies” were discovered to be in fact Spinel. For example, the enormous “Ruby” that forms the centerpiece of the royal crown of England (the Black Prince’s Ruby) was actually determined to be Spinel.