What does it mean if a mineral has good cleavage?

When a mineral is described as having good cleavage, it means that it breaks smoothly along specific planes of weakness in its crystal structure. This property is a result of the arrangement of atoms within the mineral, which typically allows the mineral to split easily along certain directions. Cleavage is characterized by flat surfaces that create clean breaks, which can often be observed in the formation of the mineral.

For instance, common minerals like mica exhibit excellent cleavage by splitting into thin, flat sheets. The presence of good cleavage is important for identifying minerals and understanding their physical properties. It can also influence how the mineral will be used in various applications, such as in the production of certain materials where smooth surfaces are beneficial.

The other options refer to different properties of minerals: the ability to be scratched relates to hardness, density refers to the mineral's mass per unit volume, and resistance to weathering pertains to how minerals respond to environmental factors. Each of these properties can indeed be used to describe minerals, but they do not relate directly to the concept of cleavage.