Weathering

The rate at which rocks disintegrate depends both on the type of rock involved and the external forces to which the rock is exposed. As an example, sandstone tends to weather rather easily, while granite is quite resistant to weathering. The presence of moisture, high temperatures, large temperature variations, and air movement also tend to increase the rate at which weathering takes place. Human activities can also affect the rate of weathering. For example, large quantities of gaseous oxides are produced by electrical power generating plants. When these oxides react with water vapor in the air, they form "acid rain." When acid rain falls to the earth's surface, it may attack rocky materials in much the same way that natural acids like carbonic acid do.