Minerals and Metals in Ancient India v2.c43.s3.t12.3

v2.c43.s3.t12.3

The approximate composition of red coral (in percentage values) is: CaCO₃ 87.0, MgCO₃ 6.8, CaSO₄ 1.3, Fe₂O₃ 1.7, Organic matter 1.35, water 0.6, and the rest, phosphate, silica, etc. 1.3. The exact composition varies with the age of the coral and other factors. With advancement in age, the coral hardens and assays higher in the percetage of MgCO₃. The amount of organic matter, which is the principal cause of colour, is much higher in black coral (above 3 per cent), which cobtains less iron (0.8 per cent). The colouring constituent is decomposed on heat, and this could be an organic compound with iron complexed in it.