report about rocks

8/11/2019 report about rocks

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ROCKS,THE

ROCK CYCLEAND ROCK

MECHANICS


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The Rock Cycle


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Igneous rock forms

when magma cools andcrystallize.

Magma is a hot liquidmade of melted minerals.

These minerals formcrystals when they cool.


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Igneous rock can form

underground, where themagma cools slowly.

Or, igneous rock canform above ground,where the magma coolsquickly.


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On Earth's surface, wind and

water can break rock intopieces.

They can also carry rockpieces to another place.These pieces of rocks, known

as sediments, drop from thewind or water to make a

layer.


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The layer can be buried under

other layers of sediments.After a long time thesediments can be cementedtogether to make sedimentaryrock.

In this way, igneous rock canbecome sedimentary rock.


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Due to the Earths heat

generating mechanisms (heatfrom friction, pressure, andradioactive decay), a rock (all of

the rocks) can be heated, hence,baked.

Rocks subjected to heat (baked),do not melt. But, changes occursdue to the heat applied to the

rocks they form crystals.


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The change in the rock/s is

called metamorphosis, and sothese rocks are termedmetamorphic rocks.

Metamorphosis/Metamorphismcan occur in rock when they

are heated to 300 to 700degrees Celsius.


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IGNEOUS ROCKS

The term igneous comes to usfrom the Latin word "Ignis"

which means fire.Most igneous rocks are

produced deep undergroundby the cooling and hardeningof magma.


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Magma is molten (melted)

rock under the surface of theEarth.

It is produced in the upperreaches of the mantle or in thelowest areas of the crustusually at a depth of 50 to 200kilometers.


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The lava that reaches the

surface through volcanoes orfissures cool down andharden, thus forming what

are called EXTRUSIVE /VOLCANIC IGNEOUS ROCKS.


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Molten rock is also cooling and thushardening into igneous rocks deepunder the surface of the Earth.

These rocks become visible becausemountain building has thrust themupward and erosion has removed thesofter rocks exposing the muchharder igneous rocks.


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These are called INTRUSIVE or

PLUTONIC igneous rocks because themagma has intruded into pre-exitingrock layers.

Intrusive igneous rocks usually takea few thousand years to coolwhereas extrusive igneous rocks takeonly a few days or weeks to cool and

solidify.


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CHEMISTRY OF VOLCANICROCKS

Mafic rocks silica poorigneous rocks with relatively

high content magnesium, ironand calcium.

MAFIC magnesium andferric.


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Basalts are dark colored, fine-grained extrusive rock. The mineral

grains are so fine that they areimpossible to distinguish with thenaked eye or even a magnifying

glass. They are the most widespread of all

the igneous rocks. Most basalts are

volcanic in origin and were formedby the rapid cooling and hardeningof the lava flows.


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FELSIC ROCKS

Silica rich igneous rocks withrelatively high amount ofpotassium and sodium.

FELSIC meaning there is highamount of feldspar, whichcrytallizes from the potassium,

sodium, aluminum and siliconoxides.


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Rhyolite is very closely related togranite. The difference is rhyolitehas much finer crystals. Thesecrystals are so small that they cannot be seen by the naked eye.

Rhyolite is an extrusive igneousrock having cooled much more

rapidly than granite, giving it aglassy appearance. The mineralsthat make up rhyolite are quartz,

feldspar, mica, and hornblende.


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INTERMEDIATE ROCKS

Intermediate rocks arethose extrusive igneous

rocks with chemicalcontent between that of

a felsic and mafic.e.g. ANDESITE


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ANDESITE
http://en.wikipedia.org/wiki/Image:Amygdaloidal_andesite.jpg


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OTHER VOLCANIC IGNEOUSROCKS


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Obsidian is volcanic glass.

It is one of the few rocks that is notcomposed of minerals.

When obsidian breaks it fractureswith a distinct conchoidal fracture.

Ancient people throughout the worldhave used obsidian for arrowheads,knives, spearheads, and cutting tools

of all kinds. Today obsidian is used asa scalpel by doctors in very sensitiveeye operations.


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Pumice is a very light colored,

frothy volcanic rock. Pumice isformed from lava that is full ofgas.

The lava is ejected and shotthrough the air during aneruption. As the lava hurtles

through the air it cools and thegases escape leaving the rockfull of holes.


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Pumice is so light that it

floats on water.Pumice is ground up and used

today in soaps, abrasive

cleansers, and also inpolishes.


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SCORIA

An extrusive igneous rock,that is a highly VESICULAR

BASALT.A vesicular rock has the

appearance of Swiss cheese.

It contains more gas thanrock.


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PLUTONIC ROCKS

Igneous rocks that are formed atgreat depth.

Pluton an igneous body thatcrystallized at a considerabledepth.

STOCK a small discordantpluton with an outcrop area ofless than 100 sq. kilometers


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BATHOLITH


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STOCK


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BATHOLITH a large discordant

pluton, with an outcrop area ofmore than 100 sq. kilometers.

A discordant igneous rockbody cuts across the pre-exitingrock bed.Batholiths and dikes are

examples of discordant rockbodies.


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A dike is a vertical or nearvertical intrusive igneousrock body that cuts acrossrock beds.

They frequently form fromexplosive eruptions thatcrack the area around avolcano with the magmafilling the cracks forming a

dike.


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A concordant igneous rockbody runs parallel to the pre-existing bedrock.

Laccoliths and sills are

examples of concordantigneous rock bodies. A laccolithis a dome shaped intrusive

body that has intrudedbetween layers of sedimentaryrock.


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The rising magma forces the

overlying layers to rise upinto a dome.

A sill is similar to a dike with

the exception that sills runparallel to the existing rock

bed instead of cuttingthrough it.


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Gabbrosare mafic, dark-colored,coarse-grained intrusive igneousrocks.

They are very similar to basalts

in their mineral composition.Gabbros are composed mostly of

the mineral plagioclase feldspar

with smaller amounts ofpyroxene and olivine.


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GRANITE

A felsic, coarse grainedigneous rock composed

mainly of potassium andsodium rich feldspar andquartz, is the most abundant

intrusive rock


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DIORITE

A coarse grained, igneousrock of intermediate

composition.It is composed of

approximately equal amountsof plagioclase feldspar andferromagnesian minerals.


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SEDIMENTARY ROCKS

Sedimentary Rocks are formed bydeposition of either detrital or organicmatter, or chemical precipitates

(evaporites), followed by compactionof the particulate matter andcementation.

Rocks that are formed from lithificationof sediments, precipitation fromsolution, or consolidation of plant or

animal remains.
http://en.wikipedia.org/wiki/Evaporitehttp://en.wikipedia.org/wiki/Evaporite


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Rocks are weathered in two ways:chemically, and mechanically,which involves erosion by rivers,wind, waves, or glaciers.

The weathered product, orsediment, will comprise fragmentsof rock and dissolved chemicalswhich can be transported intolakes, seas, oceans, or otherdepressions on the Earth's surface,where it may accumulate in layers.

SEDIMENTARY ROCKS


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SEDIMENTARY ROCKS areimportant. They are widely

spread and many of them areeconomically important, suchas coal and limestone.

Concentrated in these arerocks are important resources

such as petroleum,groundwater, and iron ore.


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SEDIMENT is the collectivefor loose, solid particles thatoriginate from:

a. weathering and erosion

from preexisting rocks.b. chemical precipitation

from solution, includingsecretion by organisms inwater.

TRANSPORTATION OF


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TRANSPORTATION OFSEDIMENTS

ROUNDING is the grinding awayof sharp corners of rockfragments during transportation.

SORTING is a process in whichsediment grains are selected andseparated according to grain size

(or grain shape or specificgravity).


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DEPOSITION

Deposition occurs whentransported material comesto rest or settles.

It also refers to theaccumulation of chemical or

organic sediment. (e.g. clamshells on the sea floor)


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LITHIFICATION

Lithification is the group ofprocesses that convert loose

sediment into sedimentaryrocks.

Cementation, compaction, and

crystallization of minerals aresome of these processes.


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TYPES OF

SEDIMENTARY

ROCKS

CLASTIC SEDIMENTARY


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CLASTIC SEDIMENTARYROCKS

Formed from cementedsediment grains that are

fragments of preexistingrocks.


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Breccia's rock fragments are very

sharp and angular.These rock fragments have not

been transported by water, wind,

or glaciers long enough to berounded and smoothed like inthe conglomerate.

The cementing agents silica,calcite (CaCO3), and iron oxidesare the same as in conglomerate.


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Conglomerate is a clasticsedimentary rock that forms fromthe cementing of rounded cobbleand pebble sized rock fragments.

Conglomerate is formed by rivermovement or ocean wave action.

The cementing agents that fill the

spaces to form the solid rockconglomerate are silica, calcite, oriron oxides.


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Sandstone is a clasticsedimentary rock that forms

from the cementing together ofsand sized grains forming a solidrock.

Quartz is the most abundantmineral that forms sandstone.

Calcium carbonate, silica, or ironhas been added to the water thatis in contact with the sand

grains.


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These minerals grow crystals

in the spaces around the sandgrains. As the crystals fill thegaps the individual sand

grains are now transformedinto a solid rock.

FINE GRAINED ROCKS


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FINE-GRAINED ROCKS

SHALE is a fine

grained sedimentaryrock notable for its splitting capability,or fissility.

Most shales contain both silt and clayand are so fined grained that thesurface of the rock feels very smooth.

These silts and clay deposits lithify and

transform into shale, and accumulateon lake bottoms, at the ends of rivers indeltas, beside rivers in flood, and onquiet part of the deep ocean floor.


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SILTSTONE is a rock consistingmostly of silt grains.

It lacks the fissility of andlaminations of shale because it ismuch more coarse-grained than

shale. MUDSTONE is a rock that contains

both silt and clay, has the same grain

size and is almost as smooth as shalebut lacks that of shales fissility andlamination.


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Li t i th t b d t f


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Limestone is the most abundant ofthe non-clastic sedimentary rocks.

Limestone is produced from themineral calcite (calcium carbonate)and sediment. The main source of

limestone is the limy ooze formed inthe ocean.

The calcium carbonate can be

precipitated from ocean water or itcan be formed from sea creaturesthat secrete lime such as algae andcoral.

COQUINA is a variety of


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COQUINA is a variety oflimestone that forms from thecementation of shells thataccumulated on sea floor.

It is usually coarse grained,due to the presence of shellsand shell fragments present

in it.


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OOLITIC LIMESTONE a


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OOLITIC LIMESTONE, avariety of limestone, is

formed through thecementation of sand-sized

oolites (ooids), small spheresof calcite inorganicallyprecipitated in warm, shallow

sea water.


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Chalk is another type of

limestone that is made up ofvery small single-celledorganisms. Chalk is usually

white or gray in color.Limestone can easily be

dissolved by acids.


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OTHER SEDIMENTARY ROCKS


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OTHER SEDIMENTARY ROCKS


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Chert is a very hard sedimentary

rock that is usually found innodules in limestone.

Chert is light gray to dark gray incolor. It probably formed from theremains of ancient sea sponges or

other ocean animals that havebeen fossilized.


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Silica has replaced the tissue

forming the sedimentary rock.Flintis a very dark form of chert.It breaks like obsidian with

conchoidal fractures making itwidely used by ancient people to

make arrowheads, spear heads,and knives.


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Organic sedimentary rocks

form from the build up anddecay of plant and animalmaterial. This usually formsin swamp regions in whichthere is an abundant supply

of growing vegetation andlow amounts of oxygen.


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METAMORPHIC ROCKS


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METAMORPHIC ROCKS

Metamorphism the solid state transformation of

preexisting rocks intotexturally or mineralogicallydistinct new rock as a result

of high temperature, highpressure, or both.

FACTORS CONTROLLING THE


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FACTORS CONTROLLING THECHARACTERISTICS OF

METAMORPHIC ROCKS

1. Composition of the parent

rock before metamorphism2. Temperature and pressure

during metamorphism

3. Effects of fluids, such aswater

CLASSIFICATION OF


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METAMORPHIC ROCKS

FOLIATED or NONFOLIATED

FOLIATION the parallel alignment oftextural and structural features of a

rock.1. If a rock splits easily along nearly flat and

parallel planes, indicating that preexisting,

microscopic, platy minerals were pushed intoalignment during metamorphism, then therock is slaty, or it possesses a slatycleavage.

2 If i ibl l t dl h d


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2. If visible platy or needle shapedminerals have grown essentiallyparallel to one another while under theinfluence of directed pressure, the rockis schistose.

3. If the rock became very plastic andthe new minerals separated into

distinct layers or lenses, the rock has alayered gneissic texture.

TYPES OF METAMORPHISM


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TYPES OF METAMORPHISM

CONTACT/THERMALMETAMORPHISM metamorphism inwhich high temperature is thedominant factor.

REGIONAL/DYNAMOTHERMAL

METAMORPHISM

metamorphismcaused by relatively high temperatureand pressure.


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Marble is metamorphosed limestone


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por dolomite. Both limestone and

dolomite have a large concentrationof calcium carbonate (CaCO3). Marblehas many different sizes of crystals.

Marble has many color variances dueto the impurities present atformation. Some of the different

colors of marble are white, red, black,mottled and banded, gray, pink, andgreen.

Marble is much harder than its parent


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Marble is much harder than its parentrock. This allows it to take a polish

which makes it a good material foruse as a building material, makingsink tops, bathtubs, and a carving

stone for artists. Today, headstones are made from

marble and granite because both ofthese rocks weather very slowly andcarve well with sharp edges.


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Slate is a fine-grained metamorphic rock


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Slate is a fine grained metamorphic rockwith perfect cleavage that allows it to split

into thin sheets. Slate usually has a light to dark brown

streak. Slate is produced by low grademetamorphism, which is caused by

relatively low temperatures and pressures. Slate has been used by man in a variety of

ways over the years. One use for slate

was in the making of headstones or gravemarkers. Slate is not very hard and can beengraved easily.


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Schist is a medium grade metamorphic


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Schist is a medium grade metamorphicrock, which means that it has been

subjected to more heat and pressure thanslate, which is a low grade metamorphicrock.

The individual grains of minerals can beseen by the naked eye, and many of theoriginal minerals have been altered into

flakes. Because it has been squeezedharder than slate it is often found foldedand crumpled.

S hi t ll d b th


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Schists are usually named by the

main mineral from which they areformed. Bitotite mica schist,hornblende schist, garnet mica

schist, and talc schist are someexamples of this


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Gneiss is a high grade metamorphic


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Gneiss is a high grade metamorphicrock, which means that gneiss has

been subjected to more heat andpressure than schist.

Gneiss is coarser than schist and hasdistinct banding. This banding hasalternating layers that are composedof different minerals.

The minerals that compose gneiss arethe same as granite.

Feldspar is the most important


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mineral that makes up gneiss along

with mica and quartz.Gneiss can be formed from a

sedimentary rock such as sandstone

or shale, or it can be formed from themetamorphism of the igneouse rockgrantite. Gneiss can be used by man

as paving and building stone.


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Quartzite is composed of


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Quartzite is composed ofsandstone that has been

metamorphosed.

Quartzite is much harder than

the parent rock, sandstone. Itforms from sandstone that hascome into contact with deeply

buried magmas. Quartzite lookssimilar to its parent rock.

The best way to tell quartzite


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The best way to tell quartzite

from sandstone is to breakthe rocks. Sandstone willshatter into many individual

grains of sand while quartzitewill break across the grains.

NAME

(Examples)CAUSE LOCATION CHARACTERISTICS


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( p )

Sedimentary

limestone;

sandstone;chalk; coal;

rock salt;

shale;

dolomite;

conglomerate

created when layers of

sediment (mud, sand, graveland minerals) settle to the

bottom of the ocean and then

compacted (pressed together)

over thousands of years

where oceansor bodies of

water once

existed or still

exist

soft, layered,

may contain

fossils

Igneous

quartz;

pumice;

granite; basalt;

obsidian

created when molten rock

(lava) inside the Earth pushes

through the crust (like in a

volcanic eruption) and then

cools

where

volcanoes have

or do exist

crystalline,

glossy, coarse-

grained

Metamorphic

marble; slate;

gneiss; schist;

created when sedimentary or

igneous rocks undergo

metamorphosis (change)

deep within theearth (where

pressure and

heat have a

hard, may

contain bands

or layers, may

report about rocks

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