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


Sedimentary


Form from lava or magma
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/conte
nt/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/visualizatio
ns/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_scienc
e/terc/content/visualizations/es0607/es0607
page01.cfm?chapter_no=visualization
Garnet biotite gneiss
Thank you!