Weathering Rates

your car, iron oxides weather more easily than iron itself. You could get voids in certain rocks where oxides have washed away.

The main oxidized substances you'll see are hematite, which is gray or red, goethite, which is brown, and limonite, which is yellow. These are cementing substances that can bind and cause coloration of sedimentary rock. All of the cool layers you'll see at the Grand Canyon and Zion National Parks come from oxidation of iron cementing these layers.

Erosion is mechanical in nature; it involves things like gravity, water, ice, or wind. Most of the time, it is liquid water that causes the mechanical erosion seen on earth. Many interesting geological features are a part of erosion and weathering. You already know that there are different resistances to weathering, depending on the rock type. The Grand Canyon and the Hoodoos seen in Bryce Canyon National Park are all major features related to erosion differences between different rock layers.

WEATHERING RATES

Which things control the rate of weathering the most? There are several factors to consider, including these:

• What are the properties of the parent rock? As you know, mafic rock weathers faster than felsic rock minerals. Water and calcite cause dissolution of the calcite more than you'll see feldspar dissolve, simply by the solubility of the compound in water. Larger granite rocks have fewer cracks than sedimentary rock, so these will not weather as much. There are more places on Earth for water to weather sedimentary rock compared to igneous rocks.

• What is the climate like? High rainfall levels and higher temperatures mean that rocks will weather more easily. This means that weathering is faster in hot, tropical environments.

• What is the soil like? Soils will generally retain water, meaning that rocks with soil on top of them have more weathering. This is because most weathering is chemical and needs water to do this. Also, you'll see bacteria and other