The Rock Cycle

Meththika Vithanage, Ph.D

What is a rock?

Definition

is a naturally occurring solid aggregate of minerals

The scientific study of rocks is called petrology

Three basic rock types

Igneous

Form from lava or magma

Sedimentary

form from sediment and chemical precipitation from seawater

Metamorphic

form from other rocks that recrystallize under higher pressures and/or temperatures

Formation of igneous rocks

Igneous rocks

Igneous rocks are formed when molten magma cools and are divided into two main categories:

plutonic rock

Volcanic rock

Plutonic or intrusive rocks result when magma cools and crystallizes slowly within the Earth's crust (example granite)

Volcanic or extrusive rocks result from magma reaching the surface either as lava or fragmental ejecta (examples pumice and basalt)

http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page05.cfm

Plutonic rocks

Volcanic rocks

Sedimentary rocks Sedimentary rocks are formed by deposition of either clastic

sediments, organic matter, or chemical precipitates (evaporites), followed by compaction of the particulate matter and cementation during digenesis.

Sedimentary rocks form at or near the Earth's surface.

Mud rocks comprise 65% (mudstone, shale and siltstone); sandstones 20 to 25% and carbonate rocks 10 to 15% (limestone)

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0605/es0605page01.cfm?chapter_no=visualization

Clastic sedimentary rocks

Clastic rocks are composed of fragments, or clasts, of pre-existing rock

Sandstone

Mudstone

Evaporites

Evaporite is a name for a water-soluble mineral sediment that result from the evaporation from an aqueous solution and has been concentrated by evaporation.

There are two types of evaporate deposits, marine which can also be described as ocean deposits, and non-marine which are found in standing bodies of water such as lakes.

Gypsum

Halite

Metamorphic rocks

Metamorphic rocks are formed by subjecting any rock type - protolith (including previously formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed.

These temperatures and pressures are always higher than those at the Earth's surface and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by recrystallisation).

high temperatures and pressures associated with the process of metamorphism

Metamorphism

http://www.classzone.com/books/earth_science/terc/content/visualizations/es0607/es0607page01.cfm?chapter_no=visualization

Garnet biotite gneiss

Thank you!