I have collected this species from the trawl catch from Gujarat state India. The collection site is located on the north western coast of India in Arabian sea
Even I am not a coral systematic researcher (see for that Prof. Michel PICHON / Queensland Brisbane Museum) it looks like a juvenile colony of Dendrophyllia (or Tubastrea) micrantha. It is naturally a "black" coloured hard coral Scleractinian. I saw the same on work stones along the Mayotte I. coast (near the Harbour). That species tolerate very turbid coastal waters, but it lives deeper in clear lagoonal waters.
Can you tell whether it was alive when you collected it and if there were any soft parts with a particular colour? I agree with Ernesto that information on depth range may help. Close-up pictures of the calices are also useful.