Coral Mangalsutra is worn by Karnataka and Andhra part of south Indian ladies. The coral is used along with black beads in various combinations to arrive at artistic designs. South Indian mangalsutra designs are heavily inspired to be lightweight to promote wearing daily. It consists of a single or double strands that is thin. It has an infuse of gold and black beads, that make it look attractive.
Have a look at these varied designs
See antique Mangalsutra designs here