Sedimentary Rocks

Types and Classification

Detritial or ClasticDerived from the weathering of pre-existing rocks, which have been transported and deposited.Occur in layers sometimes – never wavy

Detritial or ClasticDetritial Rocks are classified by grain size.– Gravel: Grain

size greater than 2 mm

• If rounded clasts = conglomerate

• If angular clasts = breccia

BrecciaConglomerate

Detritial or ClasticSand: Grain size 1/16 to 2 mm – Sandstone

Detritial or ClasticSilt: Grain size 1/256 to 1/16 mm (gritty) – Siltstone

Detritial or ClasticClay: Grain size less than 1/256 mm (smooth) – Shale (if fissile –

• splits easily) – Claystone (if massive)

Chemical or Biochemical

These rocks form from chemical components dissolved in the seawater. These chemicals may be removed from seawater and made into rocks by chemical processes, or with the assistance of biological processes (such as shell growth).

Chemical and BiochemicalEvaporites form from evaportation of water, usually seawater– Rock Salt –

composed of halite (NaCl)

– Rock Gypsum – composed of gypsum

Salt Flats in Salt Lake City, UT

Layered Gypsum, NM

Gypsum Crystals, Australia

Chemical and Biochemical1. Carbonates - The carbonate sedimentary

rocks are formed through both chemical and biochemical processes. They include the limestones (many types) and dolostones.

1. Two minerals are dominant in carbonate rocks: 1. Calcite (CaCO3) 2. Dolomite (CaMg(CO3)2)

2. Carbonate rock names: 1. Fossiliferous limestone 2. Coquina 3. Chalk

Chemical and Biochemical

Limestone

Organics (Coals)This group consists of rocks composed of organic matter (mainly plant fragments).Because of this, they lack minerals (which must be inorganic, be definition).These are the coals. In order of increasing depth of burial (temperature and pressure):– Peat – Bituminous– Anthracite

Metamorphic Rocks

Types and Classification

Metamorphic RocksMetamorphic rocks are rocks that have "morphed" into another kind of rock.The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change. If you exam metamorphic rock samples closely, you'll discover how flattened some of the grains in the rock are.

How do Rocks Change?Metamorphism causes changes in

– Texture• Recrystallization

– Growth of new crystals– Orientation of crystals - FOLIATION

• Compaction1. The grains move closer together.2. The rock becomes more dense.3. Porosity is reduced.

– Mineralogy – formation of new minerals

Foliated Metamorphic Rocks

Alignment of minerals – evident in bands or layers, may be wavy!

Non Foliated MetamorphicNo noticable layers

MarbleQuartzite

Changing Rocks

Slate - MetamorphicShale - Sedimentary

Common Metamorphic RocksClassification Metamorphic

RockParent Rock Common Minerals

Foliated (Banded)

Slate Shale, mudstone Quartz, clay minerals (feldspars)

Schist Shale, slate, basalt, or granite Mica, chlorite, talc, quartz

Gneiss Shale, schist, granite, sandstone, and other rock types

Quartz, feldspars

Non-Foliated(Not Banded)

Quartzite Sandstone Quartz

Marble Limestone, dolomite Calcite

Anthracite coal Bituminous coal Crystalline carbon