matter and minerals - geology...

1

Minerals and Rocks Tillery – Chapter 19

Science 330 Summer 2005

Matter and MineralsMatter and Minerals

2

Minerals: Building blocks of Minerals: Building blocks of rocksrocks

By definition a mineral isBy definition a mineral isNaturally occurringNaturally occurringInorganicInorganicSolidSolidOrdered internal molecular structureOrdered internal molecular structureDefinite chemical compositionDefinite chemical composition

RockRockA solid aggregate of mineralsA solid aggregate of minerals

Composition of mineralsComposition of minerals

ElementsElementsBasic building blocks of mineralsBasic building blocks of mineralsOver 100 are known (92 naturally Over 100 are known (92 naturally occurring)occurring)

AtomsAtomsSmallest particles of matterSmallest particles of matterRetains all the characteristics of an Retains all the characteristics of an elementelement

3


Atomic structureAtomic structureCentral region called the Central region called the nucleusnucleus

–– Consists of Consists of protonsprotons (+ charges) and (+ charges) and neutronsneutrons ((-- charges)charges)

ElectronsElectrons–– Negatively charged particles that surround Negatively charged particles that surround

the nucleusthe nucleus–– Located in discrete energy levels called Located in discrete energy levels called

shellsshells

Structure of an atomStructure of an atom

4


Chemical bondingChemical bondingFormation of a compound by combining Formation of a compound by combining two or more elementstwo or more elements

Ionic bondingIonic bondingAtoms gain or lose outermost (Atoms gain or lose outermost (valencevalence) ) electrons to form ionselectrons to form ionsIonic compounds consist of an orderly Ionic compounds consist of an orderly arrangement of oppositely charged ionsarrangement of oppositely charged ions

Halite (NaCl) Halite (NaCl) –– An example of An example of ionic ionic bondingbonding

5


Covalent bondingCovalent bondingAtoms share electrons to achieve Atoms share electrons to achieve electrical neutralityelectrical neutralityGenerally stronger than ionic bonds Generally stronger than ionic bonds Both ionic and covalent bonds typically Both ionic and covalent bonds typically occur in the same compoundoccur in the same compound

Covalent bondingCovalent bonding

6


Other types of bondingOther types of bondingMetallic bondingMetallic bonding

–– Valence electrons are free to migrate among Valence electrons are free to migrate among atomsatoms

–– Weaker and less common than other bondsWeaker and less common than other bonds


Isotopes and radioactive decayIsotopes and radioactive decayMass numberMass number = sum of neutrons + = sum of neutrons + protons in an atomprotons in an atomIsotopeIsotope = atom that exhibits variation in = atom that exhibits variation in its mass numberits mass numberUnstable isotopes emit particles and Unstable isotopes emit particles and energy in a process known as energy in a process known as radioactiveradioactivedecaydecay

7

Structure of mineralsStructure of minerals

Minerals consist of an orderly array of Minerals consist of an orderly array of atoms chemically bonded to form a atoms chemically bonded to form a particular crystalline structureparticular crystalline structureInternal atomic arrangement in ionic Internal atomic arrangement in ionic compounds is determined by ionic sizecompounds is determined by ionic size

Geometric Geometric packing packing

of various of various ionsions

Figure 3.8

8

Structure of mineralsStructure of minerals

PolymorphsPolymorphsMinerals with the same composition but Minerals with the same composition but different crystalline structuresdifferent crystalline structuresExamples include diamond and Examples include diamond and graphitegraphite

Phase change = one polymorph Phase change = one polymorph changing into another changing into another

Diamond and graphite Diamond and graphite –– polymorphs of carbonpolymorphs of carbon

9

Physical properties Physical properties of mineralsof minerals

Primary diagnostic propertiesPrimary diagnostic propertiesDetermined by observation or Determined by observation or performing a simple testperforming a simple testSeveral physical properties are used to Several physical properties are used to identify hand samples of mineralsidentify hand samples of minerals


Crystal formCrystal formExternal expression of a mineral’s internal External expression of a mineral’s internal structurestructureOften interrupted due to competition for Often interrupted due to competition for space and rapid loss of heatspace and rapid loss of heat

10

A garnet crystalA garnet crystal

Cubic crystals of pyriteCubic crystals of pyrite

11


LusterLusterAppearance of a mineral in reflected lightAppearance of a mineral in reflected lightTwo basic categoriesTwo basic categories

–– MetallicMetallic–– NonmetallicNonmetallic

Other descriptive terms include vitreous, Other descriptive terms include vitreous, silky, or earthysilky, or earthy

Galena (PbS) displays metallic lusterGalena (PbS) displays metallic luster

12

Physical properties of mineralsPhysical properties of minerals

ColorColorGenerally unreliable for mineral Generally unreliable for mineral identificationidentificationOften highly variable due to slight Often highly variable due to slight changes in mineral chemistrychanges in mineral chemistryExotic colorations of certain minerals Exotic colorations of certain minerals produce gemstonesproduce gemstones

Quartz (SiOQuartz (SiO22) exhibits a variety of colors) exhibits a variety of colors

13


StreakStreakColor of a mineral in its powdered formColor of a mineral in its powdered form

HardnessHardnessResistance of a mineral to abrasion or Resistance of a mineral to abrasion or scratchingscratchingAll minerals are compared to a standard All minerals are compared to a standard scale called the scale called the Mohs scale of hardnessMohs scale of hardness

Streak is obtained on an unglazed porcelain Streak is obtained on an unglazed porcelain plateplate

14

Mohs scale of

hardness


CleavageCleavageTendency to break along planes of weak Tendency to break along planes of weak bondingbondingProduces flat, shiny surfacesProduces flat, shiny surfacesDescribed by resulting geometric shapesDescribed by resulting geometric shapes

–– Number of planesNumber of planes–– Angles between adjacent planesAngles between adjacent planes

15

Common cleavagedirections

Fluorite, halite, and calciteFluorite, halite, and calciteall exhibit perfect cleavageall exhibit perfect cleavage

16


FractureFractureAbsence of cleavage when a mineral is Absence of cleavage when a mineral is brokenbroken

Specific GravitySpecific GravityWeight of a mineral / weight of an equal Weight of a mineral / weight of an equal volume of watervolume of waterAverage value = 2.7Average value = 2.7

Conchoidal fractureConchoidal fracture

17


Other propertiesOther propertiesMagnetismMagnetismReaction to hydrochloric acidReaction to hydrochloric acidMalleabilityMalleabilityDouble refractionDouble refractionTasteTasteSmellSmellElasticityElasticity

Mineral groupsMineral groups

Nearly 4000 minerals have been namedNearly 4000 minerals have been namedRockRock--forming mineralsforming minerals

Common minerals that make up most of Common minerals that make up most of the rocks of Earth’s crustthe rocks of Earth’s crustOnly a few dozen membersOnly a few dozen membersComposed mainly of the 8 elements that Composed mainly of the 8 elements that make up over 98% of the continental crustmake up over 98% of the continental crust

18

Elemental abundances in continental crustElemental abundances in continental crust


SilicatesSilicatesMost important mineral groupMost important mineral group

–– Comprise most rockComprise most rock--forming mineralsforming minerals–– Very abundant due to large % of silicon and Very abundant due to large % of silicon and

oxygen in Earth’s crustoxygen in Earth’s crustSiliconSilicon--oxygen tetrahedronoxygen tetrahedron

–– Fundamental building blockFundamental building block–– Four oxygen ions surrounding a much smaller Four oxygen ions surrounding a much smaller

silicon ion silicon ion

19

Two illustrations

of theSi–O

tetrahedron


Joining silicate structuresJoining silicate structures•• Single tetrahedra are linked together to form Single tetrahedra are linked together to form

various structures includingvarious structures including–– Isolated tetrahedraIsolated tetrahedra–– Ring structuresRing structures–– Single and double chain structuresSingle and double chain structures–– Sheet or layered structuresSheet or layered structures–– Complex 3Complex 3--dimensional structuresdimensional structures

20

Three types of silicate structuresThree types of silicate structures


Common silicate mineralsCommon silicate mineralsLight silicates: Light silicates: Feldspar groupFeldspar group

–– Most common mineral groupMost common mineral group–– Exhibit two directions of perfect cleavage at Exhibit two directions of perfect cleavage at

90 degrees90 degrees–– OrthoclaseOrthoclase (potassium feldspar) and (potassium feldspar) and

PlagioclasePlagioclase (sodium and calcium feldspar) are (sodium and calcium feldspar) are the two most common membersthe two most common members

21

Potassium feldsparPotassium feldspar

Plagioclase feldsparPlagioclase feldspar

22


Common silicate mineralsCommon silicate mineralsLight silicates: Light silicates: QuartzQuartz

–– Only common silicate composed entirely of Only common silicate composed entirely of oxygen and siliconoxygen and silicon

–– Hard and resistant to weatheringHard and resistant to weathering–– Conchoidal fractureConchoidal fracture–– Often forms hexagonal crystalsOften forms hexagonal crystals


Common silicate mineralsCommon silicate mineralsLight silicates: Light silicates: MuscoviteMuscovite

–– Common member of the mica familyCommon member of the mica family–– Excellent cleavage in one directionExcellent cleavage in one direction–– Produces the “glimmering” brilliance often Produces the “glimmering” brilliance often

seen in beach sandseen in beach sand

23


Common silicate mineralsCommon silicate mineralsLight silicates: Light silicates: Clay mineralsClay minerals

–– Clay is a general term used to describe a Clay is a general term used to describe a variety of complex mineralsvariety of complex minerals

–– Clay minerals all have a sheet or layered Clay minerals all have a sheet or layered structurestructure

–– Most originate as products of chemical Most originate as products of chemical weatheringweathering


Common silicate mineralsCommon silicate mineralsDark silicates: Dark silicates: Olivine groupOlivine group

–– High temperature FeHigh temperature Fe--Mg silicatesMg silicates–– Individual tetrahedra linked together by iron Individual tetrahedra linked together by iron

and magnesium ionsand magnesium ions–– Forms small, rounded crystals with no Forms small, rounded crystals with no

cleavagecleavage

24


Common silicate mineralsCommon silicate mineralsDark silicates: Dark silicates: Pyroxene groupPyroxene group

–– Single chain structures involving iron and Single chain structures involving iron and magnesiummagnesium

–– Two distinctive cleavages at nearly 90 Two distinctive cleavages at nearly 90 degreesdegrees

–– AugiteAugite is the most common mineral in the is the most common mineral in the pyroxene grouppyroxene group


Common silicate mineralsCommon silicate mineralsDark silicates: Dark silicates: Amphibole groupAmphibole group

–– Double chain structures involving a variety of Double chain structures involving a variety of ionsions

–– Two perfect cleavages exhibiting angles of Two perfect cleavages exhibiting angles of 124 and 56 degrees124 and 56 degrees

–– HornblendeHornblende is the most common mineral in is the most common mineral in the amphibole groupthe amphibole group

25

Hornblende amphiboleHornblende amphibole

Cleavage angles:Cleavage angles:

26


Important nonsilicate mineralsImportant nonsilicate mineralsTypically divided into classes based on Typically divided into classes based on anionsanionsComprise only 8% of Earth’s crustComprise only 8% of Earth’s crustOften occur as constituents in Often occur as constituents in sedimentary rockssedimentary rocks

27


Important nonsilicate mineralsImportant nonsilicate mineralsCarbonatesCarbonates

–– Primary constituents in limestone and Primary constituents in limestone and dolostonedolostone

–– CalciteCalcite (CaCO(CaCO33) and ) and dolomite dolomite CaMg(COCaMg(CO33))22 are are the two most important carbonate mineralsthe two most important carbonate minerals


Important nonsilicate mineralsImportant nonsilicate mineralsMany nonsilicate minerals have economic Many nonsilicate minerals have economic valuevalueExamplesExamples

–– HematiteHematite (oxide mined for iron ore)(oxide mined for iron ore)–– HaliteHalite (halide mined for salt)(halide mined for salt)–– SphaleriteSphalerite (sulfide mined for zinc ore)(sulfide mined for zinc ore)–– Native copperNative copper (native element mined for (native element mined for

copper)copper)

28

Native copperNative copper

OlivineOlivineyellowyellow--green, translucent green, translucent and glassy lookingand glassy lookingCrystals are not common; Crystals are not common; it usually occurs as it usually occurs as rounded grains in igneous rounded grains in igneous rocks or as granular rocks or as granular massesmassesalmost as hard as quartzalmost as hard as quartzdoes not have a welldoes not have a well--developed cleavage. developed cleavage.

29

QuartzQuartzglassy looking, transparent or glassy looking, transparent or translucenttranslucentvaries in color from white and varies in color from white and grey to smokygrey to smokyindividual crystals are generally individual crystals are generally clear, while in larger masses clear, while in larger masses quartz looks more milky whitequartz looks more milky whiteHardness = 7:can easily scratch Hardness = 7:can easily scratch a steel knife bladea steel knife bladeIn many rocks, quartz grains are In many rocks, quartz grains are irregular in shape because irregular in shape because crystal faces are rare and quartz crystal faces are rare and quartz does not have a does not have a cleavagecleavage

FeldsparFeldsparthe other common, lightthe other common, light--colored colored rockrock--forming mineralforming mineralgenerally dull to opaque with a generally dull to opaque with a porcelainporcelain--like appearancelike appearanceColor varies from red, pink, and Color varies from red, pink, and white (white (orthoclaseorthoclase) to green, ) to green, grey and white (grey and white (plagioclaseplagioclase))Hardness = 6: can be scratched Hardness = 6: can be scratched by quartzby quartzIn igneous rocks, forms wellIn igneous rocks, forms well--developed crystals which are developed crystals which are roughly rectangular in shaperoughly rectangular in shapeCleaves along flat facesCleaves along flat facesgrains often have straight edges grains often have straight edges and flat rectangular faces, some and flat rectangular faces, some of which meet at right anglesof which meet at right angles

30

MicaMica

easily distinguished by its easily distinguished by its characteristic of peeling characteristic of peeling into many thin flat smooth into many thin flat smooth sheets or flakessheets or flakescleavage planes are in cleavage planes are in only one direction (no right only one direction (no right angle faces)angle faces)white and pearly white and pearly ((muscovitemuscovite) or dark and ) or dark and shiny (shiny (biotitebiotite) )

PyroxenePyroxenemost common pyroxene most common pyroxene mineral is mineral is augiteaugiteAugite is generally dark Augite is generally dark green to black in colorgreen to black in colorforms short, stubby forms short, stubby crystals which, if you look crystals which, if you look at an endat an end--on section, have on section, have square or rectangular square or rectangular crosscross--sections sections

31

AmphiboleAmphibolemost common amphibole most common amphibole is hornblendeis hornblendeHornblende is quite similar Hornblende is quite similar to augite in that both are to augite in that both are dark mineralsdark mineralscrystals are generally crystals are generally longer, thinner and shinier longer, thinner and shinier than augitethan augitecrosscross--sections are sections are diamonddiamond--shaped shaped

CalciteCalcitevery common mineral in very common mineral in sedimentary rockssedimentary rockscommonly white to grey in colorcommonly white to grey in colorIndividual crystals are generally Individual crystals are generally clear and transparentclear and transparentHardness = 3: can be scratched Hardness = 3: can be scratched easily by a steel knife bladeeasily by a steel knife bladeIn a rock, calcite grains are often In a rock, calcite grains are often irregular to rhombirregular to rhomb--like in shapelike in shapemajor distinguishing major distinguishing characteristic: vigorous reaction characteristic: vigorous reaction with dilute hydrochloric acid with dilute hydrochloric acid

32

Clay mineralsClay minerals

Very fine grained and Very fine grained and difficult to tell apart in the difficult to tell apart in the fieldfieldCan vary in color from Can vary in color from white to grey, brown, red, white to grey, brown, red, dark green and blackdark green and blackClays are plastic and often Clays are plastic and often sticky when wet; they feel sticky when wet; they feel smooth when smeared smooth when smeared between the fingers between the fingers

MagnetiteMagnetite

Common in igneous and Common in igneous and metamorphic rocks, and metamorphic rocks, and some sediments, though some sediments, though usually in only small usually in only small amounts (1 amounts (1 -- 2 %)2 %)Black in color with a Black in color with a metallic lustermetallic lustersmall octahedra (like two small octahedra (like two pyramids stuck together)pyramids stuck together)strongly magnetic strongly magnetic

33

PyritePyrite

Commonest of the Commonest of the sulfide mineralssulfide mineralsOccurs in all rock Occurs in all rock types, though usually types, though usually only in small amountsonly in small amountsPale brassy yellow in Pale brassy yellow in colour with a metallic colour with a metallic lusterlusterOften forms cubeOften forms cube--shaped crystalsshaped crystals"fool's gold""fool's gold"

TalcTalc

occurs in granular occurs in granular or foliated masses or foliated masses (= “(= “soapstone”)soapstone”)white to green, white to green, sometimes grey or sometimes grey or brownishbrownishvery soft (H=1): will very soft (H=1): will be scratched by a be scratched by a finger nailfinger nailgreasy feel greasy feel

34

Minerals: The Building Minerals: The Building Blocks of RocksBlocks of Rocks

Rock (definition)Rock (definition)

Any solid mass of mineral or mineralAny solid mass of mineral or mineral--like like matter that occurs naturally as part of our matter that occurs naturally as part of our planetplanetMost rocks are aggregates of several kinds Most rocks are aggregates of several kinds of mineralsof mineralsMinerals are joined in such a way that the Minerals are joined in such a way that the properties of each mineral are retainedproperties of each mineral are retained

35

MineralMineral--forming forming ProcessesProcesses

IntroductionIntroduction

–– MagmaMagmaMolten rock from which minerals are formedMolten rock from which minerals are formed

–– LavaLavaMagma that is forced to the surfaceMagma that is forced to the surface

–– Influences on the mineral forming processInfluences on the mineral forming processTemperatureTemperaturePressurePressureTimeTimeAvailability and concentration of ions that are in Availability and concentration of ions that are in solutionsolution

36

Minerals Formed at High TemperaturesMinerals Formed at High Temperatures–– Bowen’s Reaction SeriesBowen’s Reaction Series

Arranged with minerals at the top that crystallize Arranged with minerals at the top that crystallize at higher temperature and minerals at the bottom at higher temperature and minerals at the bottom that crystallize out at lower temperature.that crystallize out at lower temperature.

Bowen's reaction series. Minerals at the top of the Bowen's reaction series. Minerals at the top of the series (olivine, series (olivine, augiteaugite, and calcium, and calcium--rich plagioclase) rich plagioclase) crystallize at higher temperatures, leaving the magma crystallize at higher temperatures, leaving the magma enriched in silica. Later, the residual magma cools and enriched in silica. Later, the residual magma cools and lighterlighter--colored, less dense minerals (orthoclase colored, less dense minerals (orthoclase feldspar, quartz, and white mica) crystallize. Thus, feldspar, quartz, and white mica) crystallize. Thus, granitelikegranitelike rocks can form from a magma that would rocks can form from a magma that would have produced basaltic rocks had it cooled quickly.have produced basaltic rocks had it cooled quickly.

37

Minerals Formed at Normal TemperaturesMinerals Formed at Normal Temperatures–– These form at normal temperatures and pressures These form at normal temperatures and pressures

and in contact with atmospheric gases such as and in contact with atmospheric gases such as oxygen, carbon dioxide, and water.oxygen, carbon dioxide, and water.

–– There are most of the nonThere are most of the non--silicates; carbonates, silicates; carbonates, sulfates, oxides, halides, and sulfides.sulfates, oxides, halides, and sulfides.

Altered MineralsAltered Minerals–– These minerals undergo changes in chemistry or These minerals undergo changes in chemistry or

crystal structure as a result of pressure, crystal structure as a result of pressure, temperature, or chemical solutionstemperature, or chemical solutions

–– Similar to minerals that form under high Similar to minerals that form under high temperatures with similar physical properties.temperatures with similar physical properties.

38

Ore MineralsOre Minerals–– Some minerals are left over after the crystallizing of Some minerals are left over after the crystallizing of

magmamagma–– These elements are flushed away in hot water These elements are flushed away in hot water

solutions as the magma crystallizes.solutions as the magma crystallizes.–– Usually crystallize in rock fractures to form thin, flat Usually crystallize in rock fractures to form thin, flat

bodies of mineral material called veins.bodies of mineral material called veins.–– If these minerals have some economic value they If these minerals have some economic value they

are called ore minerals.are called ore minerals.

IntroductionIntroduction–– Elements are chemically combined to form mineralsElements are chemically combined to form minerals–– Minerals are physically combined to form rocks.Minerals are physically combined to form rocks.

39

Igneous RocksIgneous Rocks–– Form from molten rock materialForm from molten rock material–– Intrusive igneous rockIntrusive igneous rock

Formed when magma cools deep within the Earth’s Formed when magma cools deep within the Earth’s surfacesurfaceCools very slowly as it is in contact with molten rock.Cools very slowly as it is in contact with molten rock.Produces courseProduces course--grained igneous rock.grained igneous rock.

–– Extrusive igneous rockExtrusive igneous rockMagma that cools above the Earth’s surface.Magma that cools above the Earth’s surface.Produces fineProduces fine--grained igneous rocks.grained igneous rocks.This rapid cooling does not allow time for crystals to form.This rapid cooling does not allow time for crystals to form.

Igneous rock classification scheme based on mineral Igneous rock classification scheme based on mineral composition and texture. There are other blends of composition and texture. There are other blends of minerals with various textures, many of which have minerals with various textures, many of which have specific namesspecific names

40

Granite is a coarseGranite is a coarse--grained igneous rock composed grained igneous rock composed mostly of lightmostly of light--colored, lightcolored, light--density, density, nonferromagnesian minerals. The earth's continental nonferromagnesian minerals. The earth's continental areas are dominated by granite and by rocks with the areas are dominated by granite and by rocks with the same mineral composition of granitesame mineral composition of granite

This is a piece of obsidian, which has the same This is a piece of obsidian, which has the same chemical composition as the granite. Obsidian has a chemical composition as the granite. Obsidian has a different texture because it does not have crystals and different texture because it does not have crystals and is a volcanic glass. The curved fracture surface is is a volcanic glass. The curved fracture surface is common in common in noncrystallinenoncrystalline substances such as glass.substances such as glass.

41

Sedimentary RocksSedimentary Rocks–– Form from material from previously existing rockForm from material from previously existing rock

Material is provided by weathering of previously Material is provided by weathering of previously existing rockexisting rock

–– SedimentsSedimentsWeathered rock materialsWeathered rock materialsDissolved rock materialsDissolved rock materials

–– Clastic sedimentsClastic sedimentsAnother name for weathered rock materialsAnother name for weathered rock materials

This is a sample of breccia, a coarseThis is a sample of breccia, a coarse--grained grained sedimentary rock with coarse, angular sedimentary rock with coarse, angular fragments. Compare the grain sizes to the fragments. Compare the grain sizes to the centimeter scalecentimeter scale

42

This is a sample of sandstone, a sedimentary rock that This is a sample of sandstone, a sedimentary rock that formed from sand grains in a matrix of very fineformed from sand grains in a matrix of very fine--grained silt, clay, or other materials. The grains in this grained silt, clay, or other materials. The grains in this sample are mostly the feldspar and quartz minerals, sample are mostly the feldspar and quartz minerals, which probably accumulated near the granite from which probably accumulated near the granite from which they were erodedwhich they were eroded

This is a sample of limestone, a sedimentary rock This is a sample of limestone, a sedimentary rock made of calcium carbonate that formed under water made of calcium carbonate that formed under water directly or indirectly from the actions of plants and directly or indirectly from the actions of plants and animals. This fineanimals. This fine--grained limestone formed indirectly grained limestone formed indirectly from the remains of tiny marine organisms.from the remains of tiny marine organisms.

43

–– Chemical sedimentsChemical sedimentsAnother name for dissolved rock material.Another name for dissolved rock material.The dissolved materials are ions from mineral The dissolved materials are ions from mineral and rocks that have been completely broken and rocks that have been completely broken down.down.Removed from solution by:Removed from solution by:

––Chemical precipitation from the solutionChemical precipitation from the solution––Crystallization from evaporating water.Crystallization from evaporating water.––Biological sediments.Biological sediments.

–– CompactionCompactionAs sediments are laid down grain by grain, the mass As sediments are laid down grain by grain, the mass becomes greater.becomes greater.The increasing mass of the sediment layer above creates The increasing mass of the sediment layer above creates pressure on the layers below.pressure on the layers below.Eventually this pressure becomes great enough to Eventually this pressure becomes great enough to compact the existing layers into a cohesive rock layer.compact the existing layers into a cohesive rock layer.

–– CementationCementationAfter, or during, the compaction process, the spaces After, or during, the compaction process, the spaces between the sediment particles become filled with a between the sediment particles become filled with a chemical deposit.chemical deposit.This deposit holds the compacted layers into a cohesive This deposit holds the compacted layers into a cohesive mass of sedimentary rock.mass of sedimentary rock.

44

(A)In compaction, (A)In compaction, the sediment grains the sediment grains are packed more are packed more tightly together, tightly together, often by overlying often by overlying sediments, as sediments, as represented by the represented by the bricks. (B) In bricks. (B) In cementation, fluids cementation, fluids contain dissolved contain dissolved minerals that are minerals that are precipitated in the precipitated in the space between the space between the grains, cementing grains, cementing them together into a them together into a rigid, solid mass.rigid, solid mass.

Metamorphic RocksMetamorphic Rocks–– Rocks changed by heat, pressure, or hot solutions Rocks changed by heat, pressure, or hot solutions

due to:due to:Movement of the Earth’s crustMovement of the Earth’s crustHeat generated by intrusion of hot magmaHeat generated by intrusion of hot magmaPressure can change rock by flattening, deforming, or Pressure can change rock by flattening, deforming, or realigning mineral grains.realigning mineral grains.

–– FoliationFoliationWhen the pressure on flat crystal flakes tends to align the When the pressure on flat crystal flakes tends to align the flakes into parallel sheets.flakes into parallel sheets.Gives the rock the property of breaking along the planes Gives the rock the property of breaking along the planes between the aligned mineral grains in what is known as between the aligned mineral grains in what is known as rock cleavage.rock cleavage.

45

Increasing metamorphic change occurs with Increasing metamorphic change occurs with increasing temperatures and pressures. If the increasing temperatures and pressures. If the melting point is reached, the change is no melting point is reached, the change is no longer metamorphic, and igneous rocks are longer metamorphic, and igneous rocks are formedformed

This is a sample of marble, a coarseThis is a sample of marble, a coarse--grained grained metamorphic rock with interlocking calcite crystals. metamorphic rock with interlocking calcite crystals. The calcite crystals were The calcite crystals were recrystallizedrecrystallized from limestone from limestone during metamorphismduring metamorphism

46

This banded This banded metamorphic rock is metamorphic rock is very old; at an age of very old; at an age of 3.8 billion years, it is 3.8 billion years, it is probably among the probably among the oldest rocks on the oldest rocks on the surface of the earth.surface of the earth.

The The Rock Rock CycleCycle

47

Earth is a dynamic planet with the surface and Earth is a dynamic planet with the surface and interior in a constant state of flux.interior in a constant state of flux.–– Internal changes alter the surface by moving the Internal changes alter the surface by moving the

Earth’s plates, building mountains.Earth’s plates, building mountains.–– Seas advance and retreat over the continents Seas advance and retreat over the continents

brining in new materials and taking other materials brining in new materials and taking other materials away.away.

–– Rocks are continually being changed by Earth’s Rocks are continually being changed by Earth’s forces.forces.

The The Rock CycleRock Cycle describes the continually describes the continually changing structure of rocks.changing structure of rocks.–– Igneous, sedimentary, or metamorphic rock are just Igneous, sedimentary, or metamorphic rock are just

temporary stages in the continuing changes that all temporary stages in the continuing changes that all rocks undergo.rocks undergo.

48

A schematic diagram of the rock cycle concept:A schematic diagram of the rock cycle concept:–– geologic processes act continuously to produce new rocks geologic processes act continuously to produce new rocks

from old ones.from old ones.

End of ChapterEnd of Chapter

matter and minerals - geology...

Documents