Types of Sandstone

Sandstone Formation

• Sandstone is formed from bonded or cemented grains that might be either fragments of existing rock, or minerals. Typically, these grains are calcite, clays and silica. Sandstone is usually formed by sedimentation that occurs as a result of a fluid, such as a river or a lake, in environments where sand accumulates such as sandy beaches, floodplains and deltas. Geologists gather information from sandstone samples to determine the geologic history of a particular region. Fossils are commonly found in sandstone, making it useful for paleontologists as well. Sandstone is composed of different chemicals and rock fragments, and it is typically categorized as three main types.

Arkosic

• Sandstone that contains more than 25 percent feldspar grains is called arkosic sandstone. The composition of this type of sandstone is similar to granite. Arkosic sandstone's high feldspar composition indicates that it has spent a short time in its depositional basin (place where sediments accumulate) because feldspar typically weathers rapidly, turning to clay if it sits long enough.

Quartzose

• Quartzose sandstones typically have a quartz content of greater than 90 percent. This type of sandstone is also called beach sand or quartzite, and its high quartz composition suggests that the rock has spent a long period of time in its depositional basin. Typically, this type of sandstone is white, but it may be a variety of colors such as red, depending on the conditions in which it forms. Quartzose sandstone is marked with ripples, and is commonly found in central North America and Australia.

Argillaceous

• Argillaceous sandstone, also called wacke or greywacke, has a considerable amount of clay or silt content. It has a smoother texture in comparison to quartzose or arkosic sandstone. Almost all of this type of sandstone is formed in the sea and is dark in color with a mixture of rock fragments, feldspar and quartz along with large amounts of mud (15 to 40 percent). This type of sandstone is typically found in areas where rapid erosion occurs and where the climate is temperate or arid.