Ask-A-Geologist Question: Why are some rocks easier to weather?

Weathered Rock

Today’s Ask-A-Geologist question is about rock weathering. Weathering can cause subtle or dramatic changes in the appearance of  a rock. Here is the question submitted by one of our readers:

Question:   Why are some rocks easier to weather than others?

Answer:   Weathering is the process of breaking down a rock into smaller pieces. Rain, wind snow, ice, heat and cold all affect rocks by causing physical or chemical weathering. Rocks can also physically weather by bumping into other rocks while rolling down a river or by roots growing through a rock and cracking it apart. Rocks can also weather by chemical processes. A good example of a common chemical weathering is when limestone rocks dissolve in acidic water. Some rocks are more susceptible to weathering than others because they are not as strong or hard. For example, a soft limestone that reacts to acid will weather much faster than a hard granite that does not dissolve. A weak conglomerate sample will break apart more easily than a hard basalt if they are blown by wind and carried down a river. For more information on the effects of weathering, visit this weathering article on Dig Into Geology.

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