Rocks There are three main types of Rocks A. Igneous Rocks B. Sedimentary Rocks C. Metamorphic Rocks Each type of rock is formed in different locations and tell us a lot about the processes that have happened in the past.

Rock formation occurs in the lithosphere. Different rocks form in different locations A rock on the surface may have once been 20 km underground.

The Rock Cycle

All rocks on earth are a part of a large process called the Rock Cycle All rocks on earth are a part of a large process called the Rock Cycle. In this cycle, rocks are created and changed by different processes.

The Rock Cycle It is a useful summary of the relationships between rocks. Any type of rock can be transformed in any other type of rock and has probably happened many times in the rocks history. Several key processes change rocks Weathering: the physical and chemical breakdown of rock. Transportation: the transportation of from the weathering site Deposition: the deposition of sediments after transportation Lithification: sediments turning into rock by the processes of compaction and cementation

Melting: The heating of solid rock till it melts Metamorphism: The changing of rock by heat, pressure & chemically active fluids Crystallization: The growth of crystals from a cooling magma Uplift and exposure: The movement of rock to the surface by weathering & erosion, faulting etc

Igneous Rocks result from the crystallization of magma occur in a wide variety of forms of different shapes and sizes major subdivision is into the extrusive or volcanic rocks and the intrusive or plutonic rocks. Intrusive Igneous Formed under ground Usually medium to coarse grained texture due to slow cooling. Typically light colored. Extrusive Igneous Formed on surface glassy or fine-grained due to rapid cooling May have voids due to degassing of the magma Typically dark colored.

Extrusive (volcanic) Intrusive (plutonic)

Extrusive rocks occur as lava flows and pyroclastic ash or debris that is ejected into the air during eruptions. often occur in characteristic volcanic cones submarine lava flows form characteristic pods called pillow lava. Intrusive rocks also occur in a variety of forms. vertical sheets of igneous rock are called dykes horizontal sheets, parallel or near parallel to layering are known as sills. Fatter pods of crystalline rock are called laccoliths. Very large crystalline bodies are called batholiths.

Sedimentary Rocks formed by the lithification of unconsolidated sediments. lithification is a process of compaction and cementation The weight of overlying sediments causes sediments to be reduced in volume by 40% There is also an increase press and temp The heat causes some minerals to melt, like silica and calcite these go into solution and fill spaces between remaining grains. They then harden to form a glue or cement: cementation

Depositional Environments for Sediments

Where sediments accumulate: a- alluvial fans j- continental shelf b- Glaciers k-continental slope c- rivers l-abyss d- dunes m-reefs e- lakes f- lagoons g- esturies h-deltas i- tidal flats

Metamorphic Rocks generated by recrystallization of either igneous or sedimentary rocks by the action of any or all of the following: Pressure Temperature Pore Fluids The lower limit of metamorphic temperatures is 150 °C. The upper limit is the melting temperature when magma forms. The type of metamorphic rock is determined by the parent rock, and the P/T conditions. In general, metamorphism causes: Growth of new minerals Deformation and rotation of mineral grains Recrystallization of minerals as larger grains Production of strong brittle rocks

Metamorphic rocks are divided into several groups on the basis of the P/T conditions of formation: Burial Metamorphic Rocks: are formed under the base of immensely thick layers of sediments Regional Metamorphic Rocks: generated mainly by pressure in the roots of mountain belts. Colliding continental plates push up the mountains and alter the rock. Contact Metamorphic Rocks: occur where a mass of magma invades and bakes the rock around it. Dynamic Metamorphic Rocks: are formed along transform fault zones.

Contact Metamorphic Rocks generated mainly by temperature at the margins of igneous intrusions. Sometimes called thermal metamorphic rocks.

a-sedimentary rocks b-contact metamorphic c-burial metamorphic d-regional metamorphic e-igneous rock

Metamorphic rocks are also subdivided on the basis of there texture: Non-foliated Rocks: recrystallized texture but no preferred mineral orientation. Foliated Rocks: with strong mineral orientation and/or mineral banding or layering