Alabama Landscapes

Geology, Geologic Processes and Geologic History

Table of Contents

 
 

Sedimentary Rocks

Sedimentary rocks are composed of solidified sediment

            Sediment is loose aggregate of solids that may be

                        (i)         derived from pre-existing rocks - detritus

            (ii)        chemically deposited from water 

            (iii)       hard parts of dead organisms

 

Common Sedimentary Rocks of Alabama

Conglomerate: composed of rounded fragments > 2 mm

Sandstone: composed of sand-sized fragments (2-1/16 mm) cemented together.

Siltstone: composed of silt-sized particles (1/16-1/256 mm)

Shale: composed of clay-sized fragments (<1/256 mm) pressed together in very thin layers (or beds).

Mudstone composed of clay-sized fragments (<1/256 mm) in thick beds

Limestone: composed of calcite [CaCO3], often the remains of organisms.   Dissolved easily by natural waters

Dolomite (Dolostone): composed of dolomite [Ca,Mg(CO3)2] Similar to limestone, but does not dissolve as easily

Chert: composed of microcrystalline silica. Resistant to weathering and erosion, but often associated with easily weathered limestone and dolomite

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