What is prismatic cleavage

Some minerals do not contain zones of weakness either because all of the bonds are the same strength or the weaker bonds are not aligned within a plane. If this is the case it will not have cleavage, but rather breaks in a random and irregular fashion.

Make sure to distinguish cleavage from crystal form. Crystal form occurs as a mineral grows , while cleavage only forms as a mineral breaks. See Figure 7. A mineral may have one or more cleavage planes. Planes that are parallel are considered to be in the same direction of cleavage and should only count as one. One direction of cleavage is termed basal cleavage.

Others can be hard to determine and may require measurement of the angles. A device called a contact goniometer can be handy for doing this. It is simply a protractor with an adjustable arm on it that is used to lay along one cleavage surface while the base of the protractor is laid across another. More information on this can be found in some field guides and most mineralogy texts. One can also make simple line drawings on a sheet of paper of the various angles common to minerals and keep the sheet in your guide.

This can be used for making "eyeball comparisons" with the angles between cleavage surfaces on samples. Not all do, but these three groups are common and frequently seen, so seeing these types of cleavages is likely to mean you have one of them. See a good guide book for further information. Parting : Some minerals which do not exhibit cleavage do have a characteristic that is similar, called parting.

It occurs in minerals that are crystallographically twinned, or which have been stressed by pressure. It is usually not as well, or regularly, developed as cleavage surfaces - resembling an indistinct or poorer cleavage, and it is hard to difficult to produce in specimens.

Octahedral cleavage, Dodecahedral cleavage, or Rhombohedral cleavage, cleavage parallel to the faces of an octahedron, dodecahedron, or rhombohedron. Toggle nav Word finder Word definitions prismatic cleavage. Find the word definition Enter the word Find. The act of cleaving or splitting. Cell cleavage Biol.