They use plastic and iron pyrite for the matrix. To the untrained eye, these fake stones look like the real thing. Some silversmiths truly do not know they are putting plastic in their jewelry. One way you can tell if it is real or not is by the temperature of the stone. 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.