Caused by changes in temperature, exfoliation is the breaking off of rock in curved sheets or slabs parallel to the rock's surface. During the day, the outside of the rocks heats up and expands. The same rock cools at night, and the process repeats itself day after day, causing the rock to break off in slabs. Exfoliation, shown at left, is a common sight at Enchanted Rock State Park in Texas. Because water expands when it freezes, it can cause rocks to break apart.
Water can seep into small cracks in a rock or other substance.
When the water freezes, it expands, causing the rock to break apart. This Colorado rock formation continues to show sign of frost action resulting from long and snowy winters. Sometimes a change in the color of a rock is an indication that oxidation has occurred. One common example of oxidation is shown at left, when oxygen and iron combine to form what we know as rust. The rocks break into smaller and smaller pieces.