Coins are used in all three realms. Crystals are only used in the middle and higher realm.
[Coin currency]
10 Copper coins are equivalent to 1 silver coin.
10 silver coins are equivalent to 1 gold coin.
[Crystal currency]
10 silver crystals are equivalent to 1 red crystal.
10 red crystals are equivalent to 1 blue crystal.
10 blue crystal are equivalent to 1 violet crystal.
[Convert from coins to Crystal]
10 Gold coins are equivalent to 1 silver crystal.