Cleaving Calcite by Sophie Drouin Calcite (Calcium Carbonate) is one of the most common minerals on earth. It is a major component in calcareous sedimentary rocks (limestone) and metamorphic rocks (marble). Calcite's softness (3 out of 10 on the hardness scale for minerals) combined with it lustrous appearance makes it a good material to use for mosaics. When a mineral breaks, it does so by fracturing or cleaving. Crystals, like calcite, cleave forming what appears to be a flat crystal face. Pure crystals will cleave in parallel planes. The manner in which a crystal cleaves depends on the structure of the crystal itself. Calcite crystals have three directions of cleavage. The cleavage planes are not at right angles to each other. Instead they are angled or rombehedral. Most calcite specimens are not "pure" crystals. Instead they are combined with other minerals giving them different colors and textures. Cleaving these stones is not an exact science, but with a little practice, you will soon get a feel for how to cleave calcite with a hammer and hardie in a way which produces the results you want. Keep in mind that unlike glass or ceramics, rocks have a mind of their own. They cleave in ways determined by their crystalline structure which may - or may not - be how you would like them to break.    Cacite comes in a variety of colors. Cleave in parralel or perpendicular planes. Cleaving sometimes causes multiple cuts. Cleaving a squarish crystal, follow the visible grain. Cleaving a squarish crystal, follow the visible grain (result). Cleaving long crystals is easy. Cleaving long crystals (result. << Working With Stone Menu Return to Mosaic Rocks Shop