These properties reflect how a mineral breaks. If the surface that results on breaking of a mineral is irregular, it is referred to as fracture , and if the surface is flat, it is called cleavage . Fractures are distinguished based on the type of the resulting surface. If the surface is curved, the fracture is conchoidal . It can also be fibrous , splintery or hackly .
Cleavage is a surface usually parallel to a crystal face.
Sometimes minerals cleave along closed crystal forms producing typical cleavage. Calcite crystals often show rhombohedral cleavage. Hardness Hardness is a measure of resistance of a mineral to scratching. For measuring hardness, a non-linear scale of 10 minerals is referred to. The Moh's scale of hardness lists 10 minerals from the softest talc to the hardest diamond .