Ruby is identified for its bright red colour, being the most famed and fanciful red gemstone. Besides its bright colour, it is a most popular gem due to its hardness, durability, lustre, and curiosity. Transparent rubies of large sizes are even rarer than Diamonds. Ruby is the red kind of the mineral Corundum. Sapphire, the other gem type of Corundum, includes all colours of Corundum aside from red. In essence, Ruby is a red Sapphire, since Ruby and Sapphire are alike in all sections except for colour. However, because of the special attraction and historical point, Ruby has always been listed as an individual gemstone, and is never identified as a form of Sapphire (though some purplish-red colours may balance the line of being classified as either Ruby or Sapphire).