Here's why:

* Minerals are naturally occurring, solid substances with a defined chemical composition and a specific crystal structure.

* Calcite (CaCO3) is a carbonate mineral.

* Dolomite (CaMg(CO3)2) is also a carbonate mineral, with magnesium in its composition.

* Rhodochrosite (MnCO3) is a carbonate mineral with manganese as the primary cation.

While these minerals share some characteristics, like being carbonates, they have unique chemical compositions and crystal structures that make them distinct.