To recognize a cleavage face, look for parallel planes. The number, smoothness, and angles between cleavage planes is a major key to mineral identification. Minerals without cleavage planes tend to fracture . Fracture surfaces are generally uneven, irregular surfaces. Corundum 10 Diamond Figure 1.
Color is an important feature in some minerals, such as fluorite, pyrite, and galena.
However, many, such as calcite and quartz, have a variety of colors. Color should always be evaluated on a freshly broken surface. Streak is the tendency of many soft minerals to have a characteristic powder when dragged across a porcelain plate. This is useful when a mineral is polymorphic , such as hematite. Polymorphic minerals have different forms and colors.