Fig. 19 Vitreous luster on quartz crystal faces (Photo by John Bett)

Besides the above-mentioned description of luster there is no standard scale currently in use.

7. How a mineral parts along weaknesses in its crystal lattice is referred to as cleavage. Cleavage is often very diagnostic as a mineral identification method since weaknesses in the crystal lattice will always be consistent in the same mineral. Quartz is tightly bonded in their crystalline structure and produces no cleavage. Mica has one direction of cleavage while calcite has three directions.