Diamond/Carbon
Its incomparable hardness makes this precious stone an appropriate symbol for durability and constancy; its clarity yields the notions of constancy, sincerity, and innocence. The diamond is light, life, the sun. It is an emblem of purity and perfection, of invincible spiritual power, and it is the stone of commitment, faithfulness, and promise between husband and wife. Information taken from: Online Symbolism Dictionary
Diamonds are the crystallized form of carbon created under extreme heat and pressure.
Songs referenced:
Blood Roses