Where is weathering most common

Oxygen oxidizes minerals to alteration products whereas water can convert minerals to clays or dissolve minerals completely. Different minerals weather at different rates. Mafic silicates like olivine and pyroxene tend to weather much faster than felsic minerals like quartz and feldspar. Different minerals show different degrees of solubility in water in that some minerals dissolve much more readily than others.

Water dissolves calcite more readily than it does feldspar, so calcite is considered to be more soluble than feldspar. Massive rocks like granite generally to not contain planes of weakness whereas layered sedimentary rocks have bedding planes that can be easily pulled apart and infiltrated by water. Weathering therefore occurs more slowly in granite than in layered sedimentary rocks.

Rainfall and temperature can affect the rate in which rocks weather. High temperatures and greater rainfall increase the rate of chemical weathering.

Rocks in tropical regions exposed to abundant rainfall and hot temperatures weather much faster than similar rocks residing in cold, dry regions.

Soils affect the rate in which a rock weathers. Soils retain rainwater so that rocks covered by soil are subjected to chemical reactions with water much longer than rocks not covered by soil. Soils are also host to a variety of vegetation, bacteria and organisms that produce an acidic environment which also promotes chemical weathering. Minerals in a rock buried in soil will therefore break down more rapidly than minerals in a rock that is exposed to air.

The longer a rock is exposed to the agents of weathering, the greater the degree of alteration, dissolution and physical breakup. Lava flows that are quickly buried by subsequent lava flows are less likely to be weathered than a flow which remains exposed to the elements for long periods of time.

Chemical weathering is a process where minerals in a rock may be converted into clays, oxidized or simply dissolved. Silicates comprise almost all minerals in igneous rocks and are also important components in metamorphic rocks. Not all silicates, however, survive weathering processes to become incorporated into sedimentary rocks. Figure 6. For example, interlocking silicate grains in fresh granite gradually decay along crystal boundaries due to conversion to clays. Eventually cracks open around the boundaries, the rock weakens and easily disintegrates.

Water dissolves some of the solid, leaving behind an altered material and producing a solution containing substances drawn from the original solid coffee grounds. The acid rainwater than reacts with minerals on the exposed rock face.

K-5 GeoSource. PDF version. These examples illustrate physical weathering: Swiftly moving water Rapidly moving water can lift, for short periods of time, rocks from the stream bottom. Ice wedging Ice wedging causes many rocks to break.

Plant roots Plant roots can grow in cracks. Learn More. What are sedimentary rocks? What are igneous rocks? When these rocks are exposed, and the immense weight of the overburden rock above them is removed, they expand, and zones of weakness open up as joints. Granite tends to open and peel away sheets of rock think of peeling an onion ; the domes in Yosemite are formed by this process, which is called unloading. There are examples of this type of weathering in the Landslide module as well as the throughout the Weathering module.

Frost wedging. Notice how these granite rocks have been "pried" apart? Image is from Sierra Nevada Mountains. Has the sun been weathering this rock equally; though the sun is always in the Southern Hemisphere? Image is from Southeast Utah. Rock is broken into gently dipping plates by unloading joints. Unloading joints probably form as the rock is exposed by erosion.

These joints, and others that are more steeply oriented, provide pathways for water to enter the rock. Image is from Yosemite National Park in California.