This is a traditional Indian mangalsutra, a type of necklace worn by married Hindu women. It features:
Black beads strung along the chain, which are culturally believed to ward off evil.
Gold spacers or beads interspersed between the black beads, adding decorative and symbolic value.
A pendant set with red stones (likely rubies or ruby-colored gems) and a curved row of small white stones (possibly diamonds or cubic zirconia), set in gold.