Coral jewelry can be worn as beads, cabochons, cameos or carvings.
Coral, which is the exoskeleton of an animal called coral polyp, lives
in warm oceans and has been harvested and turned into coral jewelry
for many centuries. 
These
polyps exude calcium carbonate to create their protective home that
evolves into branches that may be several inches to several feet long,
but are not always thick.
Coral jewelry comes in a variety of colors ranging from white
to pink to red to blue and black. Oxblood red is one of the most valued in red
coral jewelry. It has been traced back to 3000 B.C. Salmon coral is another
variety that is also quite popular. More rare are the black and blue varieties
of coral from Hawaii and Cameroon. Some coral jewelry may contain specimens
that have been bleached and dyed.
Moh's scale of hardness classifies coral as having a hardness
of 3.5-4. This is relatively soft and can be scratched with a metal object
fairly easily. Your coral jewelry should not be cleaned with abrasive gem
cleaner, but rather warm water and a polishing cloth.
