The world's rarest gem is believed to be painite, a gem that most have never even heard of. Rarity does not equate to beauty in gems, however. The painite is an orangish or reddish brown, with the brown tint coming from iron in the crystal. It was first discovered in Burma in the 1950s and was widely considered to be the rarest of all gems, with only two faceted crystals in existence.
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety. Colors range from red to blue to mauve. Dark green, brown.