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Weather and Sediment• Physical weathering –
physical decomposition of a material (into grains or clasts).
• Chemical weathering – chemical decomposition or dissolution of a material (into a solution).
Weather and Sediment
• Sediment – loose grains/chemical residues or rocks, minerals, plants & animals
• Erosion – transport of weathered sediments
Sedimentary Rocks• Form when:
– Sediments collect, compact & harden:• Lithification
– Mineral crystals precipitate from an aqueous solution
• Sedimentary rocks are classified by:– Composition – Texture
Sedimentary Composition• Detrital (siliciclastic) –
– Rock or mineral fragments• Quartz, feldspar, clay, or lithic fragments
• Chemical – – Precipitated from aqueous solution
• Calcite, dolomite, halite, gypsum, iron bearing minerals, chert
• Biochemical (bioclasts) – – Grains are remains of organisms
• See page 116 in lab manual
Sedimentary Textures
• Grain size:
– Deposits • Gravel size > sand sized >
silt sized > clay sized
– Precipitates • Crystalline >
microcrystalline
Sedimentary Textures
• Grain shape:
– Describes the smoothness of the edges of grains
– Well rounded to angular
Sedimentary Textures
• Grain arrangement:– Describes sorting of the grains– Poorly sorted, moderately sorted, well
sorted• See page 111 in lab manual