buy gabapentin 100mg for dogs Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite and dolomite. Because the main composition of marble is calcium carbonate (CaCO3), it is much softer than granite. Marble ranks about 4 on the Mohs mineral hardness scale. It comes in a wide variety of colours and patterns. It’s also very heat-resistant (which is great as marble countertops in the kitchen), but does need regular maintenance.