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ROCK CYCLE,

SOIL DEPOSIT

AND GRAIN-SIZE

Dr. Ir. HJ. Achmad Fauzi b Abd. WahabDr. Ir. HJ. Achmad Fauzi b Abd. Wahab

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James Hutton (17271797),

the eminent 18th century gentlemanfarmer and founder of modern

geosciences, authored the concept of therock cycle, which depicts the inter-relationships between igneous,sedimentary, and metamorphic rocks.

The Rock Cycle

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The Rock Cycle

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A rockis a naturally formed, consolidated material

usually composed of grains of one or more minerals

The rock cycle shows how one type of rocky material

gets transformed into another

Representation of how rocks are formed, broken

down, and processed in response to changingconditions

Processes may involve interactions of geosphere with

hydrosphere, atmosphere and/or biosphere

Arrows indicate possible process paths within the

cycle

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The Rock Cycle and Plate

Tectonics

Convergent plate

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(1) Igneous Rocks

Magma is molten rock

Igneous rocks form when magma

cools and solidifies

Intrusive igneous rocks form whenmagma solidifies underground

Granite is a common example

Extrusive igneous rocks form whenmagma solidifies at the Earths

surface (lava)

Basalt is a common example

Granite

Basalt

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Igneous Rocks

Texture refers to the size, shape andarrangement of grains or other constituents

within a rock

Texture of igneous rocks is primarily

controlled by cooling rate Extrusive igneous rockscool quickly at or

near Earths surface and are typically fine-

grained(most crystals 1 mm)

Fine-grained I.R

Coarse-grained I.R

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Special Igneous Rocks

Pegmatitic I.R

Porphyritic I.R

A pegmatite is an extremely coarse-grainedigneous rock (most crystals >5 cm) formed

when magma cools veryslowly at depth

A glassy texture contains no crystals at all,

and is formed by extremely rapid cooling A porphyritic texture includes two distinct

crystal sizes, with the larger having formed

first during slow cooling underground and

the small forming during more rapid coolingat the Earths surface

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Igneous Rocks Identification

Igneous rock names are based on texture (grain size) andmineralogy composition

Textural classification

Plutonic rocks (gabbro-diorite-granite) are coarse-grained and cooled

slowly at depth Volcanic rocks (basalt-andesite-rhyolite) are typically fine-grained and

cooled rapidly at the Earths surface

Compositional classification

Mafic rocks (gabbro-basalt) contain abundant dark-colored

ferromagnesian minerals

Intermediate rocks (diorite-andesite) contain roughly equal amounts of

dark- and light-colored minerals

Felsic rocks (granite-rhyolite) contain abundant light-colored minerals

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Igneous Rocks Identification

I.R.

names are

based on

texture(grain size)

&

Mineralogic

composition

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Six common Igneous Rocks

Solidifying Temperature 500 C1000 C

Increasing Grain Size

Volcanic

Rocks

Silica

Content

Minerals Present(in order of abundance)

Plutonic

Rocks

Basalt low pyroxene, olivine,feldspar, & amphibole

Gabbro

Lighter

Co

lor

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Rock types and tectonic

setting

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(2) Sedimentary Rocks

are formed bypressure, heat,and drying out.Sediments do not

necessarily haveto be undertremendouspressure to

becomesedimentary rock(as seen in the

lab).

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Sedimentary Rocks (cont)

The Earths Crust is made up of solidbedrock. (Bedrock is solid rock that isconnected continuously down into theEarths crust, rather than existing asseparate pieces or masses surrounded byloose materials

Sedimentary Rockare by far themost common rock type in theupper crust

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Rocks are broken down by weathering

Sediment is transported by wind, water,or glaciers to a new site, where it is

deposited in layers. Over time, thesediments are buried and pressedtogether, or compacted.

Eventually, the sediment is cemented

together to form new rocks, know assedimentary rock.

This process takes millions of years

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Sedimentary Rockusuallylayered, that results fromthe consolidation orlithification of sediment, forexample a clastic rock likesandstone or a chemicalrock like rock salt, or an

organic rock like coal (U8). Sedimentary Rock are either

Marine (deposited in theocean) or nonmarine

(deposited on thecontinents). If marinesedimentary rock arepresent, the area must have

been below sea level.

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Physical andChemicalprocesses worktogether toconvert exposedbedrock

Siliciclastic andChemical

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Clastic fragments of rocks & minerals that havebeen physically transported & deposited & thenconverted into rock

Chemical Direct precipitation of minerals from asolution. Only chemical sedimentary rocks areaffected by chemical (vinegar/acid), all others arenot affected, unless the acid is strong enough.

Organic- Remains of plants and animals that have

been converted into rock

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Clastic Sedimentary Rocks

Clastic Sedimentary Rock: asedimentary rock made up ofmostly of fragments derivedfrom pre-existing rocks andtransported mechanically totheir places of deposition.

Clastic Sedimentary Rock aremade up mostly of fragments,called clasts that are erodedfrom other rocks.

Clay or Mud (Smallest 1/16 mmor smaller

Sand (1/16 to 2 mm)

Gravel (pebbles to boulders,

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Chemical Sedimentary Rocks

Rocks consist ofmaterials that haveprecipitated from theocean water or lake

water (Utah or DeathValley). Remember-Only chemicalsedimentary rocks are

affected by chemicals Precipitation: the

process of formingsolid mineral

constituents from asolution by

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Chemical Sedi. Rocks (cont)

a sedimentary rockconsisting mainly ofthe remains oforganisms (U10).

Consists of the

mineral calcite, acalcium carbonatemineral with theformula CaCO3

Organic SedimentaryRock forms whenplants in swamps withrich vegetation dieand are buried by the

remains of laterplants

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(3) Metamorphic Rocks

is rocks that have been exposed togreat heat and pressure.

A.A. Dynamic Metamorphism(RegionalDynamic Metamorphism(Regional

Metamorphism):Metamorphism):

large areas of rock are under greatheat and pressure.

Ex: mountain building.

B. ,,,,,,,

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Pressure squeezes grains closertogether, creating a denserand

less porous rock.

Heat and chemicals mayrearrange

particles (atoms). Minerals arereformed or new ones are formed.

Ex: QuartziteQuartzite was once

sandstone;sandstone;

B. How heat and pressure causerocks

to change:

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C. Characteristics of MetamorphicRocks

FoliationFoliation grains are in parallellayers. Ex: slate. Gneiss is the

coarsestfoliation of all metamorphic rocks.

BandingBanding bands of light coloredminerals alternate with bands of dark

colored minerals.

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D.Thermal Metamorphism (contactmetamorphism) Igneousintrusionsbake overlying rock.

The changes are less drastic thanregional metamorphism and foliationis not produced.

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Banding

GRANITE

GNEISS

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Documents

Rock Cycle (3-1) R1