Cleavageisthetendencyofamineraltobreakalongcertainplanestomakesmoothsurfaces.
Minerals with different crystal structures will cleave in different ways, asFigure3.16shows.
Halite tends to form cubes with smooth surfaces, mica tends to form sheets, and fluorite can
form octahedrons.
Figure 3.16: Minerals with different crystal structures have a tendency to break along certain
planes. ( 17 )
Minerals can form various shapes like the polygons, shown inFigure3.17, when they are
broken along their cleavage planes. The cleavage planes are important for people who cut
gemstones, such as diamonds and emeralds. The planes determine how the crystals can be
cut to make smooth surfaces.
Fracturedescribes how a mineral breaks when it is not broken along a cleavage plane.
All minerals break but fracture describes a break when the resulting surface is not smooth
and flat. You can learn about a mineral from the way it fractures. Jagged edges are usually
formed when metals break. If a mineral splinters like wood it may be fibrous. Some minerals,