Sedimentary Rocks

Sediments

Are loose, unconsolidated rock particles and ions (i.e., charged atoms) dissolved in aqueous solutions.

Sedimentary Rocks

Constitute about 75% of all rocks exposed at the surface of the Earth, form when the particles are cemented together or when crystals precipitate from the solutions.
Are important (particularly sandstone) because they host petroleum deposits and most of the uranium used for generating nuclear energy.

Types of Sedimentary Rocks

• Clastic (or detrital)
• Biochemical
• Chemical

Clastic Sedimantary Rocks

• Constitute more than 75% of the total sedimentary rocks.
• These rocks are formed from cemented grains and particles derived from the breakdown of preexisting rocks of any type (e.g., igneous, sedimentary, or metamorphic).
• The classification of clastic sedimentary rocks is based mainly on the size of the grains.

Conglomerate

(if the grains are rounded) A clastic sedimentary rock formed by gravel (i.e., grains bigger than 2 mm in diameter: granules, pebbles, or boulders)

Sandstone

A clastic sedimentary rock formed by grains between 1/16 and 2 mm in diameter

Sandstones

• Can be further classified according to the most abundant minerals they contain.
• Formed mostly by grains of the mineral quartz are called quartz sandstones (or quartz arenites), whereas sandstones formed mostly by grains of the mineral feldspar are called arkoses.

Graywackes

Sandstones that include high amounts of fine-grained clay

Conglomerates, Breccias, and sandstones

Are formed by grains that are coarse enough to be seen with the naked eye

Silt

Grains between 1/256 and 1/16 mm in diameter

Clay

Grains smaller than 1/256 mm in diameter) are too small to be seen with the naked eye.

Silt and clay grain

When cemented together, form the clastic rocks siltstones and claystones, respectively.

Siltstones and claystones

Are sometimes collectively called mudstones. A mudstone that easily splits in different layers is a shale.

Biochemical sedimentary rocks

Are formed from the remains of organisms.

Peat and bituminous coal

Are formed from plant fragments.

Peat

Is commonly brown and porous, with plant fragments that are still visible.

Bituminous coal

Is black without distinguishable plant remains

Fossiliferous limestone

Is formed from fossil shells and coral and is the most common biochemical sedimentary rock.

Chemical Sedimentary Rocks

These rocks are classified according to their chemical composition.
Some common chemical sedimentary rocks are limestone (formed by CaCO3), dolostone (CaMg(CO3)2), chert (SiO2), rock salt (NaCl), and rock gypsum (CaSO4·2H2O).

Sedimentary rocks

Belonging to the last type (chemical) form by precipitation from aqueous solutions.

Limestone

Is the rock that most commonly is responsible for the development of karst topography.

Chocolate Hills

Located in Bohol, a city in the Philippines, is made out of limestone, which is a type of sedimentary rock

ZAMBALES OPHIOLITE

• It basically consist of igneous, metamorphic and sedimentary rocks.
• Petrological and geochemical studies reveal that this ophiolite suite can be divided into two major units, the Coto and Acoje blocks (Hawkins and Evans, 1983; Yumul, 1989, 1990), each made up of a complete ophiolite sequence: residual (upper mantle) - transition zone – cumulate (base of crust) - volcanic (oceanic crust) rocks.

Zambales Ophiolite Complex

An east-dipping complete sequence of oceanic crust and mantle material, is located at the western portion of Central Luzon spanning 160 km N-S and 40 km at its widest (E-W) portion.