Sedimentary rocks, pt2

Sedimentary rocks

1. clastic

2. chemical

3. organic

Sedimentary rocks: chemical rocks

Sea, lake, swamp, and other waters contain dissolved minerals.

Chemical sediments are formed when these minerals fall out of solution: Evaporation Chemical reaction

Chemical rocks

1. limestones of chemical origin: from tiny grains of calcite

2. rock salt

3. gypsum

limestone

Rock salt

gypsum

Sedimentary rocks

1. clastic

2. chemical

3. organic: formed from the remains of animals and plants.

E.g. limestone and coal

limestone

usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris.

It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or ocean water.

limestone

Contain calcite, so they can be identified by the acid test.

Fossils

Fossils

Fossils are remains or impressions of plants and animals in rock

Skeletal structures remain, or are replaced by minerals in their shape.

Found in sedimentary rocks. (Why not in igneous rocks?)

geodes

geodes

1. Water dissolves some limestones, creating cavities within.

2. The groundwater deposits quartz or calcite crystals in the cavities.

concretions

concretions

Concretions are rounded rocks embedded in layers of stone in sedimentary rocks. They are often harder than the surrounding rock and weather out of the host rock. They are often spherical or nodules. Nodules are often shaped like potatoes.