You will have a subtle difference in temperature between the plastic stones and the real stones. Real stones are colder by nature than plastic. Take the time to check it out - particularly if it is an expensive piece of jewelry. Real fetish necklaces take an enormous amount of time, patience, and talent to create. Each fetish should be hand carved out of real stone.
Fetish necklaces are unique to the Zuni Tribe in New Mexico.
Find out who made the necklace and where they are from. If the business proclaims a piece to be authentic they are promising that it is sterling silver with real stones, if any. If later you discover it is not authentic, then you will have proof of deceit. It has become commonplace for a business to employ Native American silversmiths to mass produce items such as earrings, pendants, necklaces and more. The employees usually get paid an hourly wage and have the materials supplied by the business.