The natural coral grains used in Coral Calcium 1 are certified by the Japanese government, as "Food Grade".
To be certified food grade there can not be over 0.5 parts per million of any "Heavy Metal" (see the C of A). There are many cheap brands of what they are calling "Coral Calcium".
The informed customer should only buy a product that has a certificate of analysis (C of A) on display, and then only if it is the mineral rich "Marine grade".

When reading a C of A, one should look for the highest amount of naturally occurring magnesium. This is regarded as the standard of quality. There are products being sold as coral, that in reality are classified as Limestone.
These products are high in calcium, but very low in Magnesium and are very difficult for the body to absorb.