Aug 18, 2019 · Calcite vs Quartz. Calcite and quartz may look the same in some regard to appearance but they are very different. Calcite is a calcium carbonate mineral while quartz is a silie mineral with a chemical formula of SiO 2. Quartz has a hardness of 7 on the Mohs scale of hardness while Calcite is much softer at a 3.