Diamond and ruby are both gemstones that have been used for centuries in jewelry and other decorative items. They are both precious stones that are highly valued for their beauty and rarity. Diamonds are the hardest natural substance known to man, while rubies are a type of corundum that is colored red by trace elements of chromium. Both gems are cut and polished to bring out their natural beauty and sparkle. GEM is a general term for any precious or semi-precious STONE, while STONE is a broad term for any naturally occurring mineral or rock.