Apatite is a group of phosphate minerals, usually referring to hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of [tex]OH^-, F^- and Cl^-[/tex] ions, respectively, in the crystal while Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate.
The hardness value of apatite on Moh's scale is 5 while for calcite its 3.
Calcite is used primarily as construction aggregates, and in production of lime and cement while apatite is occasionally used as a gemstone and in fertilizers.
Since, Apatite serves a higher value of hardness on Moh's sacle thus they are used in scratching a mineral. Also, it is formed under a wide variety of conditions and is found in igneous, metamorphic, and sedimentary rocks.
