Sapphire : A sapphire is a mineral but it is not diamond even though a diamond is a mineral as well. They are both different types of minerals. Sapphires are a variety of the mineral corundum,which is an aluminum oxide.The remarkable hardness of sapphires, which measure 9 on the Mohs scale, is second only to diamond. That's why sapphire is one of the few gemstones that make a great alternative for an engagement ring.
Emerald : Emerald is the green to bluish green variety of beryl, a mineral species that also includes aquamarine as well as beryls in other colors. Gem experts differ on the degree of green that makes one stone an emerald and another stone a less-expensive green beryl.