MineralsMinerals

Minerals: Building blocks of rocksMinerals: Building blocks of rocks

• Definition of a Definition of a mineralmineral::• Naturally occurringNaturally occurring• Inorganic solidInorganic solid• Ordered internal molecular structureOrdered internal molecular structure• Definite chemical compositionDefinite chemical composition

• Definition of a Definition of a rock:rock:• A solid aggregate or mass of mineralsA solid aggregate or mass of minerals

Note: a rock may be mono-mineralicNote: a rock may be mono-mineralic

Composition of mineralsComposition of minerals

• ElementsElements• Basic building blocks of mineralsBasic building blocks of minerals• Over 100 are known (92 naturally Over 100 are known (92 naturally

occurring)occurring)

• AtomsAtoms• Smallest particles of matter that retains Smallest particles of matter that retains

all the characteristics of an elementall the characteristics of an element

Atomic structureAtomic structure• Central region called the Central region called the nucleusnucleus

– Consists of Consists of protonsprotons (positive charges) (positive charges) and and neutronsneutrons (neutral charges) (neutral charges)

• ElectronsElectrons– Negatively charged particles that Negatively charged particles that

surround the nucleussurround the nucleus– Located in discrete energy levels called Located in discrete energy levels called

shellsshells

Idealized Idealized structure of an structure of an

atomatom

Halite (NaCl) – Halite (NaCl) – Minerals consist of an Minerals consist of an orderly array of atoms chemically bonded to form a orderly array of atoms chemically bonded to form a

particular crystalline structureparticular crystalline structure

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

Structure of mineralsStructure of minerals

PolymorphsPolymorphs• Two or more minerals with the same Two or more minerals with the same

chemical composition but different chemical composition but different crystalline structurescrystalline structures

• Diamond and graphite are good examples Diamond and graphite are good examples of polymorphsof polymorphs

» The transformation of one polymorph to The transformation of one polymorph to another is called a phase changeanother is called a phase change

Physical properties of mineralsPhysical properties of minerals• Crystal FormCrystal Form

• External expression of the orderly External expression of the orderly internal arrangement of atomsinternal arrangement of atoms

• Crystal growth is often interrupted Crystal growth is often interrupted because of competition for space and because of competition for space and rapid loss of heatrapid loss of heat

Slow cooling in a melt makes for largeSlow cooling in a melt makes for large EUHEDRALEUHEDRAL crystals. crystals.

This garnet is an example of a This garnet is an example of a euhedral garnet.euhedral garnet.

Physical properties of mineralsPhysical properties of minerals

• LusterLuster• Appearance of a mineral in reflected lightAppearance of a mineral in reflected light• Two basic categoriesTwo basic categories

– MetallicMetallic

– NonmetallicNonmetallic

• Other terms are used to further describe Other terms are used to further describe luster such as vitreous, silky, or earthyluster such as vitreous, silky, or earthy

Galena is a lead sulfide that Galena is a lead sulfide that displays displays metallic lustermetallic luster

Physical properties of mineralsPhysical properties of minerals

• ColorColor• Generally an unreliable diagnostic Generally an unreliable diagnostic

property to use for mineral identificationproperty to use for mineral identification• Often highly variable for a given mineral Often highly variable for a given mineral

due to slight changes in due to slight changes in mineral chemistrymineral chemistry• Exotic colorations of some minerals Exotic colorations of some minerals

produce gemstonesproduce gemstones

Quartz (SiO2) exhibits a Quartz (SiO2) exhibits a variety of colorsvariety of colors

Physical properties of mineralsPhysical properties of minerals• StreakStreak

• Color of a mineral in its powdered formColor of a mineral in its powdered form• Helpful in distinguishing different forms Helpful in distinguishing different forms

of the same mineralof the same mineral

• HardnessHardness• Resistance of a mineral to abrasion or Resistance of a mineral to abrasion or

scratchingscratching• All minerals are compared to a standard All minerals are compared to a standard

scale called the scale called the Moh’s scale of hardnessMoh’s scale of hardness

Physical properties of mineralsPhysical properties of minerals

• CleavageCleavage• Tendency to break along planes of weak Tendency to break along planes of weak

bondingbonding• Produces flat, shiny surfacesProduces flat, shiny surfaces• Described by resulting geometric shapesDescribed by resulting geometric shapes

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

Three examples of perfect cleavage – Three examples of perfect cleavage – fluorite, halite, and calcitefluorite, halite, and calcite

Physical properties of mineralsPhysical properties of minerals

• FractureFracture• Absence of cleavage when a mineral is Absence of cleavage when a mineral is

brokenbroken

• Specific GravitySpecific Gravity• Ratio of the weight of a mineral to the Ratio of the weight of a mineral to the

weight of an equal volume of waterweight of an equal volume of water• Average value is approximately 2.7Average value is approximately 2.7

Conchoidal fractureConchoidal fracture

Physical properties of mineralsPhysical properties of minerals• Other propertiesOther properties

• MagnetismMagnetism• Reaction to hydrochloric acidReaction to hydrochloric acid• MalleabilityMalleability• Double refractionDouble refraction• TasteTaste• SmellSmell• ElasticityElasticity

Classification of MineralsClassification of Minerals• Nearly 4000 minerals have been identified on Nearly 4000 minerals have been identified on

EarthEarth• Rock-forming mineralsRock-forming minerals

• Common minerals that make up most of the Common minerals that make up most of the rocks of Earth’s crustrocks of Earth’s crust

• Only a few dozen membersOnly a few dozen members• Composed mainly of the 8 elements that make up Composed mainly of the 8 elements that make up

over 98% of the continental crustover 98% of the continental crust

Classification of MineralsClassification of Minerals• SilicatesSilicates

• Most important mineral groupMost important mineral group– Comprise most of the rock-forming Comprise most of the rock-forming

mineralsminerals

– Very abundant due to large Very abundant due to large amounts of silicon and oxygen in amounts of silicon and oxygen in Earth’s crustEarth’s crust

• Basic building block is the Basic building block is the silicon-silicon-oxygen tetrahedronoxygen tetrahedron molecule molecule

– Four oxygen ions surrounding a Four oxygen ions surrounding a much smaller silicon ionmuch smaller silicon ion

Common Silicate Structures

• Common Silicate Common Silicate mineralsminerals

• OlivineOlivine– High temperatureHigh temperature

Fe-Mg silicateFe-Mg silicate

– Individual Individual tetrahedra linked tetrahedra linked together by iron together by iron and magnesium and magnesium ionsions

– Forms small, Forms small, rounded crystals rounded crystals with with no cleavageno cleavage

• Common Silicate Common Silicate mineralsminerals

• Pyroxene GroupPyroxene Group– Single chainSingle chain

structures involving structures involving iron and magnesiumiron and magnesium

– Two distinctive Two distinctive cleavages at nearly cleavages at nearly 90 degrees90 degrees

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

• Common Silicate Common Silicate mineralsminerals

• Amphibole GroupAmphibole Group– Double chainDouble chain structures structures

involving a variety of ionsinvolving a variety of ions

– Two perfect cleavagesTwo perfect cleavages exhibiting angles of 124 and exhibiting angles of 124 and 56 degrees 56 degrees (120 deg, 60 deg)(120 deg, 60 deg)

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

• Common Silicate Common Silicate mineralsminerals

• Mica GroupMica Group– Sheet structuresSheet structures that that

result in result in one direction of one direction of perfect cleavageperfect cleavage

– BiotiteBiotite is the common is the common dark colored mica dark colored mica mineralmineral

– MuscoviteMuscovite is the common is the common

light colored mica minerallight colored mica mineral

• Common Silicate mineralsCommon Silicate minerals• Feldspar GroupFeldspar Group

– Most common mineral Most common mineral groupgroup

– 3-dimensional framework 3-dimensional framework of tetrahedra exhibitof tetrahedra exhibit two two directions directions of perfectof perfect cleavage at 90 degreescleavage at 90 degrees

– OrthoclaseOrthoclase (potassium (potassium feldspar) and feldspar) and PlagioclasePlagioclase (sodium and calcium (sodium and calcium feldspar) are the two most feldspar) are the two most common memberscommon members

• Common Silicate Common Silicate mineralsminerals

• Clay Clay mineralsminerals– Clay is a general Clay is a general

term used to term used to describe a variety of describe a variety of complex mineralscomplex minerals

– Clay minerals all Clay minerals all have a sheet or have a sheet or layered structurelayered structure

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

• Important non-silicate mineralsImportant non-silicate minerals• Several major groups exist includingSeveral major groups exist including

– OxidesOxides– SulfidesSulfides– SulfatesSulfates– Native ElementsNative Elements– CarbonatesCarbonates– HalidesHalides– PhosphatesPhosphates

• Important nonsilicate Important nonsilicate mineralsminerals

• CarbonatesCarbonates– Primary constituents Primary constituents

in in limestone and limestone and dolostonedolostone

– CalciteCalcite (calcium (calcium carbonate) and carbonate) and Dolomite Dolomite (calcium-(calcium-magnesium magnesium carbonate) are the two carbonate) are the two most important most important carbonate mineralscarbonate minerals

• Important nonsilicate mineralsImportant nonsilicate minerals• Many nonsilicate minerals have economic Many nonsilicate minerals have economic

valuevalue• ExamplesExamples

– 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)

Native CopperNative Copper

How else do we look at minerals?How else do we look at minerals?

• Thin-sections -- MicroscopeThin-sections -- Microscope

• Scanning Electron MicroscopeScanning Electron Microscope

• X-Ray DiffractionX-Ray Diffraction

• X-Ray FluorescenceX-Ray Fluorescence

• Mass SpectrometryMass Spectrometry

Thin SectionThin Section

Scanning Electron MicroscopeScanning Electron Microscope

X-Ray Diffraction