Sedimentary Rocks

Weathering

Erosion

Transport

Deposition

Sediments

Lithification

WeatheringThe sediments that make up sedimentary rocks are produced by:

Mechanical & Chemical Weathering

Mechanical Weathering

Chemical Weathering

MineralStability

Products of Weathering

• Lithic (Rock) Fragments(granite, basalt, schist, etc.)

• Dissolved Ions(Calcium, Potassium, Sodium, etc.)

• Rust Minerals (Hematite, Goertite, etc.)

• Clay Minerals(Bentonite, Montmorillonite, etc.)

• Residual Minerals(Quartz, Orthoclase, Muscovite, etc.)

Erosion & Transport

WaterWindIce

Gravity

Deposition

Lithification

Sediment

Rock

Cementation

Typical Cement:•Calcite•Quartz

Sedimentary RocksIdentification

Note: Use the same terms to describesediments & sedimentary rocks.

Only difference is lithification!

Rock Identification is based on:

•Composition

What minerals make up the rock?

•Texture

What is the shape, size and orientation of the mineral grains that make up the rock?

Major Difference:Crystalline vs. Clastic

Types of Sedimentary Rocks

Detrital Rocks Chemical Rocks

vs.

Difference: TextureDetrital (Clastic

Texture)

vs.

Chemical (Crystalline Texture)

Detrital Rock Composition

Detrital Rocks• Lithic Fragments• Quartz• Clay Minerals• Fossil Fragments• Rust Minerals• Orthoclase• Muscovite / Biotite

Detrital Rock Texture

Clastic Texture• Grain Size• Grain Sorting• Grain Rounding• Sediment Maturity

Grain Size

•Gravel2mm

•Sand1/16 mm

•Mud - Silt1/256 mm

•Mud - Clay

Detrital Rock Names

(Based Primarily on Grain Size)

Sand Sized: Sandstone

Gravel Sized:Conglomerate

Siltstone Shale

Mud Sized:Mudstone

Sorting

Grain Roundness

Gravel Sized Detrital Rocks

(Subdivided Based on Grain Roundness)

Breccia

Conglomerate

Maturity

Mature•Well Sorted•Well Rounded•All Quartz

Immature•Poorly Sorted•Angular grains•Mixed Compositionincluding clay

Sandstones

(Subdivided based on maturity)

Quartz SandstoneArkose (Sandstone)

Lithic Sandstone Greywacke

Sandstones Under a Scope

Clastic (Detrital) Sedimentary Rocks

Grain Size Roundness Sorting Composition Name

Rounded Moderate to

poor Fragments of any rock type CONGLOMERAT E

Gravel-sized (> 2 mm)

Angular Moderate to

poor Fragments of any rock type BRECCIA

Rounded Well All Quartz - usually white to tan QUARTZ

SANDSTONE

Sub-rounded to

Angular

Moderate to poor (few

grains >2mm)

Feldspar (usually orthoclase), micas, quartz, and other minerals

ARKOSE (Arkosic Sandstone)

Sub-rounded

Moderate to well

Quartz, lithic fragments, and other minerals

LITHIC SANDSTONE

Sand-sized (visible grains up to 2 mm)

Rounded to angular

Moderate Quartz and rock fragments mixed

with >15% clay; often gray colored GRAYWA CKE SANDSTONE

Silt-sized (feels gritty)

(to small to see)

Well Clay and quartz (but usually too

small to see) SILTSTONE

Clay (but usually too small to see); Massive

MUDSTONE Clay-sized

(feels smooth) (to small to

see) Well

Clay (but usually too small to see); Breaks into semi-flat layers

SHALE

Detrital Sedimentary Rock ID

Chemical Rock Texture

Crystalline Texture

• Coarse• Fine

Chemical Sedimentary Rocks

(Names based primarily on composition)

Basic Rock Name• Limestone• Chert• Rock Salt• Rock Gypsum• Peat or Coal

Composition• Calcite• Quartz (silica)• Halite• Gypsum• “Carbon” / Plant Remains

Chemical Rocks(Names based mainly on

composition)

LimestonesCrystallineLimestone

Chalk

Fossiliferous Limestone

Chemical Rocks (cont.)Evaportites

RockGypsum

Rock Salt

Coal

Chert

Chemical, Biochemical & Organic Sedimentary Rocks

Composition Texture Name

Crystalline - medium to coarse (visible) grains CRYSTALLINE

LIMESTONE

Crystalline - grains too small to see MICRITE

Abundant fossils in a fine- to coarse-grained crystalline matrix FOSSILIFEROUS

LIMESTONE

Calcite (acid reaction)

Fine-grained powder, earthy smell (often black, gray, or white) CHALK

Dolomite (acid reaction)

Crystalline - fine to coarse grained DOLOSTONE

Crystalline - grains too small to see; conchoidal fracture CHERT Quartz (scratches

glass) Fine-grained powder, earthy smell (no acid reaction) (often white) DIATOMITE

Gypsum Crystalline - fine to coarse grained ROCK GYPSUM

Halite (tastes salty)

Crystalline - fine to coarse grained ROCK SALT

Fibrous, brownish plant material; soft PEAT Plant Remains

(Carbon) Dense, black masses; depending on grade may be dull to vitreous; lower grades may contain minor fossils

COAL

Chemical Sedimentary Rock ID

Sedimentary Rocks on Earth