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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) compaction2) cementation
a) Lime or calcite (bubbles in acid)b) Hematite (rust or iron oxide) – Red Rocksc) Limonite – yellow brown colord) Silica – quartz, hardest of all cementse) 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 solutions3) 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 – bandedpetrified woodchert – light coloredflint – dark colored
5) Halite – evaporated saltwater deposit6) Gypsum
These two rocks make up the “evaporites”, and their mineral name is also their rock name.
ofCoquina
Coal
