This is the chemical reaction pathway of Calcium sulfide (CaS) being converted to Calcium phosphate (Ca3(PO4)2) through the following steps:

CaS is first oxidized to CaO (Calcium oxide) by reacting with oxygen:
2 CaS + 3 O2 -> 2 CaO + 2 SO2

CaO is then hydrated to form Ca(OH)2 (Calcium hydroxide) by reacting with water:
CaO + H2O -> Ca(OH)2

Finally, Calcium hydroxide (Ca(OH)2) reacts with phosphoric acid (H3PO4) to form Calcium phosphate (Ca3(PO4)2) through a double displacement reaction:
3 Ca(OH)2 + 2 H3PO4 -> Ca3(PO4)2 + 6 H2O

Thus, starting from CaS, the final product obtained is Calcium phosphate (Ca3(PO4)2) through the series of chemical reactions mentioned above.