From the Manufacturer:
OkinawanCoral featured by the world renowned expert Robert R. Barefoot, author of the book “Barefoot on Coral Calcium”. Barefoot coral calcium is below sea level collected coral, a proprietary form of coral calcium sand. High quality cora calcium. Okinawan coral remnants free of PCB's and collected with ecological safety.
Coral calcium is much more than just a source of calcium. It is a holistic mineral supplement that is rich in calcium and magnesium, but it contains more than 70 trace minerals that may be of value for general health.