Some minerals have a tendency to split or crack along parallel or flat planes. This property is easily seen in some minerals and you can test the mineral by breaking it with a hammer or splitting off sheets with a pen knife. These planes along which the mineral breaks are called cleavage planes. If the mineral splits easily along these planes the mineral is then said to have perfect cleavage. Mica is a good example of perfect cleavage. Feldspar is an example of a mineral with cleavage in more than one direction. Quartz is a mineral that has no cleavage at all. Quartz shatters likes glass when struck with a hammer. The biotite mica on the far left splits into sheets that are perfectly parallel. They form because of weak and strong bonds between the mica layers. The feldspar breaks into two planes at consistent angles.
Fracture is related to cleavage. Fracture occurs when a mineral breaks at random lines instead of at consistent cleavage planes. Many minerals that have no cleavage or poor cleavage fracture easily. The obsidian on the far right is a good example of a rock that has conchodial (glass like) fracture. Quartz is a mineral that also has conchodial fracture.
Click on the "Next" button to learn about an amazing property of two minerals!
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