The word Amulet comes from the Latin; amuletum, meaning an object to protect a person from trouble. Many things can be used as an amulet and good candidates are Gems, Stones, Statutes, Coins, Pendants, Rings, Herbs and other Plants, small animal figurines and even spoken words. However, they are generally characterised by having a form representative of their use - so they often take the form of a mystical symbol, an effigy or carry some sort of Magical inscription.
Amulets provide their powers because of what they are, whereas a Talisman is specifically given its powers of protection by being consecrated, blessed or otherwise charged with the owners intent.