Cleavage and Fracture
Many mineral crystals break in certain ways—into cubes, sheets, pyramids, or in other patterns. These patterns—called 'cleavage'—depend on the structure of atoms inside the crystal. Some kinds of atoms are joined together quite strongly. Other kinds have weak joints. The crystal will cleave (break) where the joints are weakest.

Mica cleaves into thin sheets, because the weakest joints are between flat sheets of strongly-jointed atoms.	Galena cleaves into cubes, because the joints inside are equally strong—there are no weaker joints to make it break in a different pattern.	Not all minerals cleave neatly. Some don't break in any particular way. Instead, they simply fracture into odd shapes. For example, quartz fractures into shell-like pieces.

Do you think that our golden cube will cleave or fracture?

© The Children's Museum of Indianapolis, 2000