Sedimentary rocks - lithification

Sedimentary rocks are formed through lithification. Shown in (A) are unconsolidated particles. When subjected to lithification, they become sedimentary rock shown in (B).

Classification of sedimentary rocks

Sedimentary rocks

Detrital

Chemical

Sedimentary rocks are primarily grouped into two main types according to how they were formed. Detrital sedimentary rocks were formed through physical means (pressure) while chemical sedimentary rocks were chemically formed.

Detrital sedimentary rocks – fissility

Fissility refers to the property of detrital sedimentary rocks that enables them to be split into thin sheets.

home

Detrital sedimentary rocks – sorting

home

The particles that make up detrital sedimentary rocks undergo sorting. Rocks upstream tend to be angular and poorly sorted while rocks downstream are rounded and well sorted.

Classification of sedimentary rocks

Sedimentary rocks

Detrital

Coarse (>2mm)

Medium (1/16 to 2mm)

Fine (1/16 to 1/256mm)

Very fine (less than 1/256

mm)

Chemical

home

Detrital rocks are classified according to the size of their particles.

Classification of sedimentary rocks

Coarse (>2mm) Gravel

Conglomerate (Rounded particles)

Breccia (Angular particles)

Medium (1/16 to 2mm) Sand

Quartz sandstone (little

feldspar)

Arkose (abundant feldspar)

Fine (1/16 to 1/256mm) Mud Siltstone

Very fine (less than 1/256

mm)Mud Shale

home

Classification of sedimentary rocks

Sedimentary rocks

Detrital

Chemical

Calcite, CaCO3

Quartz,

SiO2

Gypsum, CaSO4

Halite, NaCl

Plant fragments

home

Chemical sedimentary rocks are classified according to their predominant component.

Classification of sedimentary rocks

Calcite, CaCO3

Inorganic limestone Nonclastic: fine to coarse crystalline

Crystalline limestone

Travertine

Biochemical limestone

Clastic: visible shell fragments loosely

cementedCoquina

Clastic: various size coral fragments cemented with

calcite

Fossiliferous limestone

Clastic: Microscopic shells and clay ChalkCalcite rocks are grouped according to how

they were formed (inorganic or via biochemical processes). Inorganic limestones are described as nonclastic which means that they are not made of particles. Biochemical limestones on the other hand, are made of particles and so are clastic. home

Classification of sedimentary rocks

Sedimentary rocks, environments and structures

Quartz, SiO2

Nonclastic: very fine

crystalline

Chert

(light colored)

Flint

(dark colored)

Gypsum, CaSO4

Nonclastic: fine to coarse crystalline

Rock gypsum

Halite, NaClNonclastic:

Fine to coarse crystalline

Rock Salt

Plant fragments

Nonclastic: Fine-grained

organic matter

Bituminous coal

Conglomerate (detrital, gravel, rounded particles)

home

Breccia (detrital, gravel, angular particles)

home

Quartz sandstone (detrital, sand, mostly quartz)

home

Arkose (detrital, sand, abundant felspar)

home

Siltstone (detrital, fine-sized particles, mud)

home

Shale (detrital, very fine particles, mud, may contain fossils)

home

Crystalline limestone (chemical, nonclastic, fine to coarse crystalline)

home

Travertine (chemical, nonclastic, fine to coarse, cavewaters)

home

Coquina (chemical, clastic, shell fragments, loosely cemented)

home

Fossiliferous limestone (chemical, clastic, coral fragments, calcite cement)

home

Fossiliferous limestone are made of coral reef fragments cemented strongly by calcite.

Chalk (chemical, clastic, microscopic shells and clay)

home

home

Chert (chemical, nonclastic, quartz, light colored)

home

Flint (chemical, nonclastic, quartz, dark colored)

Rock gypsum (chemical, nonclastic, CaSO4)

home

Rock salt (chemical, nonclastic, NaCl, evaporite)

home

Rock salt (chemical, nonclastic, NaCl, evaporite)

home

Halites are known as evaporites because they are formed through the evaporation of water from chemically-concentrated solutions.

Coal exists in many forms. The first form is peat which is still impure and damp (and hence contains a low amount of stored energy). Peat that has undergone burial and pressure becomes lignite or bituminous coal (which is now more concentrated and hence has more energy). Anthracite is the metamorphic form of coal which is formed after intense pressure and heat.

homeCoal (chemical, nonclastic, plant remains)

Peat

home

Lignite or bituminous coal home

Bituminous coal can be metamorphosed into anthracite

home