RocksRocksand the Rock Cycleand the Rock Cycle

What is a rock?What is a rock? How does a rock form?How does a rock form? What is/are the origin(s) of a rock? What is/are the origin(s) of a rock?

Definition of a RockDefinition of a Rock

Made of mineralsMade of minerals Firm and coherent Firm and coherent Aggregate of materialsAggregate of materials

Why Study Rocks?Why Study Rocks?

Rocks and minerals have economic value. Rocks and minerals have economic value. Earth processes (volcanic eruptions, Earth processes (volcanic eruptions,

mountain building, weathering, mountain building, weathering, earthquakes etc.) depend in some ways on earthquakes etc.) depend in some ways on the properties of rocks. the properties of rocks.

Every rock contains clues about the Every rock contains clues about the environment in which it formed. By looking environment in which it formed. By looking at rocks closely we can figure out events at rocks closely we can figure out events that happened earlier in Earth history. that happened earlier in Earth history.

Components of a RockComponents of a Rock

ClastsClasts (fragments) or crystals large (fragments) or crystals large enough to see the individual pieces enough to see the individual pieces

MatrixMatrix - fine-grained material - fine-grained material between larger clasts or crystals between larger clasts or crystals

CementCement - crystalline added after the - crystalline added after the original rock formed (usually by original rock formed (usually by water flowing through the rock) water flowing through the rock)

ClastsClasts

Clasts + MatrixClasts + Matrix

Clasts + CementClasts + Cement

The Rock CycleThe Rock Cycle

Rocks are divided into three groups Rocks are divided into three groups based on their mode of origin: based on their mode of origin: – igneous, igneous, – metamorphic, metamorphic, – sedimentary. sedimentary.

Each type of rock can be linked to Each type of rock can be linked to another type by processes that act another type by processes that act on and within the Earth. on and within the Earth.

Igneous RockIgneous Rock

Sedimentary RockSedimentary Rock

Metamorphic RockMetamorphic Rock

Rock Cycle (Basic)Rock Cycle (Basic)

Magma (molten rock) Magma (molten rock) – crystallizes (cools and solidfies) at or crystallizes (cools and solidfies) at or

near the surface to form near the surface to form igneous rocksigneous rocks

Rock Cycle (Basic)Rock Cycle (Basic)

A rock, exposed at the surface A rock, exposed at the surface undergoes undergoes – weatheringweathering

disintegration of rock due to disintegration of rock due to chemical/mechanical action, chemical/mechanical action,

– transportationtransportation or or erosionerosion sediment moves downhill by gravity and sediment moves downhill by gravity and

taken somewhere else by wind or water, taken somewhere else by wind or water,

Rock Cycle (Basic)Rock Cycle (Basic)

A rock, exposed at the surface A rock, exposed at the surface undergoes undergoes – depositiondeposition

-comes to rest somewhere - in an ocean, -comes to rest somewhere - in an ocean, river floodplain, swamp, sand dune etc., and river floodplain, swamp, sand dune etc., and

– lithificationlithification conversion into rock through compaction conversion into rock through compaction

and cementation and forms a and cementation and forms a sedimentary rocksedimentary rock. .

Rock Cycle (Basic)Rock Cycle (Basic)

A rock at or near the surface is A rock at or near the surface is buried to great depth and is buried to great depth and is subjected to: subjected to: – intense heat (due to magma nearby?) or intense heat (due to magma nearby?) or – pressure (due to mountain building) pressure (due to mountain building) – The rock reacts to this change of The rock reacts to this change of

environment by becoming a environment by becoming a metamorphic rockmetamorphic rock. .

Alternate PathsAlternate Paths

The full rock cycle does not always The full rock cycle does not always take place. Some "short cuts" are: take place. Some "short cuts" are: – Sedimentary rock melts. Sedimentary rock melts. – Igneous rock is metamorphosed. Igneous rock is metamorphosed. – Sedimentary rock weathers. Sedimentary rock weathers. – Metamorphic rock weathers. Metamorphic rock weathers.

RockRockCycleCycle

(2)(2)

Plate Tectonics and the Rock Plate Tectonics and the Rock CycleCycle

Cooling and crystallization of Cooling and crystallization of magmamagma– volcanic arcs, rifts/ridges volcanic arcs, rifts/ridges

MetamorphismMetamorphism– At depth, especially within arcs At depth, especially within arcs

UpliftUplift, weathering, erosion, , weathering, erosion, depositiondeposition– Especially where mountains built up at Especially where mountains built up at

plate margins plate margins

Plate Tectonics and the Rock CyclePlate Tectonics and the Rock Cycle