Sedimentary Rocks
Sedimentary rocks form from the accumulation of sediment at earth’s surface. Most sedimentary rocks are layered. Sedimentary rocks can form from grains of pre-existing rocks (detritus), from chemical processes, or from organic processes. They are classified based on their texture and composition.
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Origins of Sedimentary Rocks (Part 1)
Sedimentary rocks can form from grains of pre-existing rocks (detritus), from chemical processes, or from organic processes.Detrital Sedimentary Rocks
Detrital sedimentary rocks form from detritus, the rock and mineral fragments that are transported by gravity, water, ice, or wind. Detrital sediments are classified by grain size.
Detritus is classified by its grain size. Grains larger than 2 millimeters are called gravel. Grains between 1/16 mm and 2 mm are called sand. Grains smaller than 1/16 mm are in the silt and clay size ranges, often referred to as mud.
Detrital sediments (Photograph by Parvinder Sethi)
Albemarle County conglomerate (Photograph by Parvinder Sethi)
This Albemarle County conglomerate is an example of a detrital sedimentary rock. It contains gravel and sand grains. Note dime for scale.