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The compaction and cementation of rock particles forms sedimentary rocks. Sedimentary Rocks are formed at or near the Earths surface. 75% of crust is covered by sedimentary rocks, yet only 10% of the crust is sedimentary. Lithification – cementing particles together involves 2 processes: 1) compaction 2) cementation a) b) c) d) e) Lime or calcite (bubbles in acid) Hematite (rust or iron oxide) – Red Rocks Limonite – yellow brown color Silica – quartz, hardest of all cements Clay – generally, a powder look 3 Types of Sedimentary Rocks 1) Clastic – made from the lithification of rock fragments. 2) Chemical precipitate – from chemicals that form out of solutions 3) Organic A) Clastic – Names are based on particle size. 1) Conglomerate – 50% or more gravel size particles. 2) Sandstone – sand sized particles of quartz 3) Arkose – sandstone made up of primarily feldspar 4) Siltstone – particles you can’t see with a naked eye. 5) Shale – made up of clay, splits into layers, smells earthy when wet. B) Chemical Precipitates – these form when 1) water evaporates, leaving the dissolved material as a sedimentary rock. 2) Small organisms with shells die, and their shells and other hard parts accumulate to form rocks. These rocks are named based on their mineral composition. 1) Limestone – made up primarily of calcite, and may contain fossils. 2) Coquina – loosely cemented shell fragments made up of calcite. 3) Travertine – calcite deposited around hot springs, usually layered in appearance. 4) Chalcedony – from the precipitation of quartz. Very hard rocks! Varieties of chalcedony: agate – banded petrified wood chert – light colored flint – dark colored 5) Halite – evaporated saltwater deposit 6) Gypsum These two rocks make up the “evaporites”, and their mineral name is also their rock name. of Coquina Coal