Minerals form crystals with specific shapes when they have been able to grow without obstruction. Common shapes are prisms, pyramids, needles, cubes, and sheets . Cleavage Minerals break along specific planes of weakness related to their atomic structure. Quartz has no cleavage planes but fractures irregularly. Moh's hardness scale Minerals are ranked from 1 to 10 based upon their relative hardness.
Harder minerals can scratch softer minerals.
Ten index minerals make up Moh's scale and other minerals are ranked relative to these. For example, a mineral that could scratch feldspar but not quartz would have a hardness of approximately 6.5. Luster Characteristics of light reflected from mineral is luster. Types of luster include earthy, silky, glassy, and metallic. Streak Minerals will leave a mark when pulled across an unglazed porcelain streak plate.