minerals and mineralogy a/prof john m. worden dec university of southern queensland

Minerals and MineralogyMinerals and Mineralogy

A/Prof John M. WordenA/Prof John M. Worden

DECDEC

University of Southern QueenslandUniversity of Southern Queensland


What is a mineral?What is a mineral? A A naturallynaturally occurring, occurring,

--solidsolid,, inorganic inorganic crystallinecrystalline substance, substance,

-with a specific-with a specific composition composition, ,

-and characteristic -and characteristic atomic structureatomic structure.. Approximately 100 minerals are common.Approximately 100 minerals are common. Of these, about 30 comprise the rock formingOf these, about 30 comprise the rock forming

minerals and make up most Crustal rocks. minerals and make up most Crustal rocks. A select group of minerals are of economicA select group of minerals are of economic

interest and these are termed interest and these are termed ““ore mineralsore minerals”. ”.


Minerals are the building blocks of rocks.Minerals are the building blocks of rocks. So, we need to briefly re-visit basic chemical concepts to understand both their So, we need to briefly re-visit basic chemical concepts to understand both their

chemistry and physical properties.chemistry and physical properties. Smallest units of matter are “Smallest units of matter are “atomsatoms” that retain physical & chemical ” that retain physical & chemical

properties of an properties of an elementelement.. Each atom has a dense “Each atom has a dense “nucleusnucleus” at its centre, containing positively charged ” at its centre, containing positively charged

““protonsprotons”” and neutral “ and neutral “neutronsneutrons”.”. The number of protons is constant for an element,The number of protons is constant for an element,

and defines its “ and defines its “atomic numberatomic number (z) (z)”” The “The “atomic massatomic mass”is the ”is the (# protons + # neutrons). (# protons + # neutrons). A cloud of moving, negatively charged “A cloud of moving, negatively charged “electronselectrons” ”

surround the nucleus.surround the nucleus. The number of electrons equals the number ofThe number of electrons equals the number of

protons, so an atom is electrically protons, so an atom is electrically neutral.neutral.


Electrons occupy Electrons occupy orbitalsorbitals,, or more simply, spherical shells around the or more simply, spherical shells around the nucleus.nucleus.

An atom’s electronic structure determines its interactions with An atom’s electronic structure determines its interactions with atoms of another element to form chemical compounds.atoms of another element to form chemical compounds.

We must examine the fine structure of electron orbitals to We must examine the fine structure of electron orbitals to understand this process.understand this process. Each orbital or electron shell can hold a specified maximum number of Each orbital or electron shell can hold a specified maximum number of

electrons (ie ,K= 2; L=8; M= 18; N= 32 etc).electrons (ie ,K= 2; L=8; M= 18; N= 32 etc). A complete outermost shell is the most stable A complete outermost shell is the most stable

configurationconfiguration In chemical reactions, In chemical reactions, ONLYONLY the electrons in the the electrons in the

outermost shells interact to attain maximum outermost shells interact to attain maximum stability.stability.

Minerals and MineralogyMinerals and Mineralogy Electrons may be exchanged between atoms of two elements thereby Electrons may be exchanged between atoms of two elements thereby

forming a new compound.forming a new compound.

For Sodium (Na; z =11) and Chlorine (Cl; z=17) atoms:For Sodium (Na; z =11) and Chlorine (Cl; z=17) atoms: Na atoms surrender their single outermost electrons leaving the next inner Na atoms surrender their single outermost electrons leaving the next inner

shell complete ( L=8), while Cl atoms accept electrons to complete part of shell complete ( L=8), while Cl atoms accept electrons to complete part of their outermost shell (M=8). Both become charged “their outermost shell (M=8). Both become charged “IONSIONS”.”.

“ “CationsCations” (Na” (Na++) and “) and “AnionsAnions” (Cl” (Cl--) are charged ions in which electron ) are charged ions in which electron shells are either depleted or supplemented.shells are either depleted or supplemented.

Ionic bonds form between anions & cationsIonic bonds form between anions & cations due to electrical attraction. due to electrical attraction. They are the dominant type (>90%) of chemical They are the dominant type (>90%) of chemical

bonding found in minerals.bonding found in minerals.

Minerals and MineralogyMinerals and Mineralogy Elements that do not readily gain or lose electrons Elements that do not readily gain or lose electrons shareshare

electrons, forming “electrons, forming “Covalent bondsCovalent bonds”” Covalent bonds are stronger than ionic bonds.Covalent bonds are stronger than ionic bonds.

An example is Diamond, where each C atom (z=6) covalently bonds with An example is Diamond, where each C atom (z=6) covalently bonds with four surrounding C atoms so that L=8, forming a regular tetrahedron.four surrounding C atoms so that L=8, forming a regular tetrahedron.

““Metallic bondsMetallic bonds” are a type of covalent bond found in native ” are a type of covalent bond found in native metals (ie Cu; Ag; Au; Te) and some sulfides.metals (ie Cu; Ag; Au; Te) and some sulfides.

““Van der WaalsVan der Waals” bonds result from weak” bonds result from weak electrostatic attraction between atoms. electrostatic attraction between atoms.

Complex ions, ie [SiOComplex ions, ie [SiO44] are strongly-bonded ] are strongly-bonded covalent pairs that act as single ions.covalent pairs that act as single ions.

All minerals are combinations of these All minerals are combinations of these bonding types in regular, repeated arrays, or crystal lattices.bonding types in regular, repeated arrays, or crystal lattices.


Minerals are grouped into 8 classes (Native elements; Oxides & Minerals are grouped into 8 classes (Native elements; Oxides & Hydroxides; Halides; Carbonates; Sulfates; & Silicates).Hydroxides; Halides; Carbonates; Sulfates; & Silicates).

By far the most dominant mineral group are the By far the most dominant mineral group are the SilicatesSilicates, based , based on the silicate ion, or [SiOon the silicate ion, or [SiO44]]4- 4- tetrahedron. The silicon ion is tetrahedron. The silicon ion is

surrounded by four oxygen ions that can bond with other ions.surrounded by four oxygen ions that can bond with other ions. Various bonding linkages result in: Various bonding linkages result in:

isolated tetrahedra; single or double chains;isolated tetrahedra; single or double chains; sheets; and 3D frameworks. sheets; and 3D frameworks.

Oxygen-Oxygen bonds are very strong,Oxygen-Oxygen bonds are very strong, whereas Oxygen-Cation bonds are much whereas Oxygen-Cation bonds are much weaker. weaker.

Minerals and MineralogyMinerals and Mineralogy The common rock-forming minerals are combinations of : Al, Fe, The common rock-forming minerals are combinations of : Al, Fe,

Ca, Na, K, and Mg with [SiOCa, Na, K, and Mg with [SiO44].]. These elements are the most abundant in the Earth’s crust.These elements are the most abundant in the Earth’s crust. Bonding types of various silicates reflect temperatures of Bonding types of various silicates reflect temperatures of

crystallisation , so that “crystallisation , so that “isolated tetrahedraisolated tetrahedra” linked through ” linked through cations form at highest temperatures, ie cations form at highest temperatures, ie OlivineOlivine..

As temperature declines, atom vibrational energies decline and As temperature declines, atom vibrational energies decline and more complex bonds result.more complex bonds result.

““Single chainSingle chain” silicate minerals form next,” silicate minerals form next, sharing two apical oxygens, ie sharing two apical oxygens, ie AugiteAugite..

Next, “Next, “Double chainDouble chain” silicates, which share” silicates, which share three apical oxygens crystallise,ie three apical oxygens crystallise,ie HornblendeHornblende..


This continues with “This continues with “SSheetheet”silicates, (mica minerals) & the”silicates, (mica minerals) & the “ “FrameworkFramework” minerals forming last, ie ” minerals forming last, ie BiotiteBiotite & & QuartzQuartz..

Crystal lattices control the external shape and surfaces of a Crystal lattices control the external shape and surfaces of a mineral. The planar surfaces are termed “mineral. The planar surfaces are termed “crystal facescrystal faces” and their ” and their combinations and “combinations and “interfacial anglesinterfacial angles”” are specific for each are specific for each mineral.mineral.

A crystal will only possess perfect form if it crystallises in a fluid A crystal will only possess perfect form if it crystallises in a fluid or in unconstrained space. or in unconstrained space.

Confinement means interlocking grain Confinement means interlocking grain boundaries and the formation of boundaries and the formation of aggregatesaggregates..


SummarySummary• Minerals must be Minerals must be naturallynaturally formed. formed.

• They must beThey must be inorganic inorganic..

• Minerals must beMinerals must be solid solid and and crystalline crystalline..

• Have a specific chemicalHave a specific chemical composition composition..• They must possess a characteristic They must possess a characteristic crystal structurecrystal structure..


Physical properties of minerals reflect the elements, bonding Physical properties of minerals reflect the elements, bonding types and crystal lattices of each mineral.types and crystal lattices of each mineral.

Physical propertiesPhysical properties include: include: ColourColour StreakStreak LustreLustre DiaphaneityDiaphaneity HardnessHardness CleavageCleavage FractureFracture TenacityTenacity Crystal FormCrystal Form TwinningTwinning Specific GravitySpecific Gravity OtherOther


Colour:Colour: Very obvious;Very obvious; Intrinsic;Intrinsic; May be due to impurities and highly unreliable, andMay be due to impurities and highly unreliable, and Note the great diversity of colours exhibited by Quartz (SiONote the great diversity of colours exhibited by Quartz (SiO22). ).

For example, amethyst, citrine, rose quartz, etc.For example, amethyst, citrine, rose quartz, etc.

Streak:Streak: The colour of a The colour of a powderpowder of a mineral. of a mineral. More reliable than that of the massive More reliable than that of the massive

mineral.mineral. Attributed to the grain size effect.Attributed to the grain size effect.


Lustre:Lustre: Quality and intensity of reflected light from a mineral surface.Quality and intensity of reflected light from a mineral surface. Subdivided into:Subdivided into:

• MetallicMetallic

• Non-metallicNon-metallic Non-metallic further subdivided into:Non-metallic further subdivided into:

• vitreous – (glass-like)vitreous – (glass-like)

• pearly – (pearl-like)pearly – (pearl-like)

• greasy- (as if covered with an oil film)greasy- (as if covered with an oil film)

• resinous – (like resin)resinous – (like resin)

• dull – (no discernible lustre)dull – (no discernible lustre)

• etc.etc.


Diaphaneity:Diaphaneity: Refers to the degree of Refers to the degree of TransparencyTransparency..

• Transparent;Transparent;

• Translucent;Translucent;

• Opaque.Opaque.

Tenacity:Tenacity: Manner in which a mineral breaks down orManner in which a mineral breaks down or

deforms under stress. deforms under stress. Most minerals are brittle and shatter!Most minerals are brittle and shatter! The micas (biotite & muscovite) are flexibleThe micas (biotite & muscovite) are flexible

and elastic. and elastic.


Hardness:Hardness: A measure of the ability of a mineral to resist abrasion or A measure of the ability of a mineral to resist abrasion or

scratching.scratching. Reflects the strength of the bonds between atoms.Reflects the strength of the bonds between atoms. Mohs Hardness ScaleMohs Hardness Scale from Talc (H=1) to Diamond (H=10). from Talc (H=1) to Diamond (H=10).

Cleavage:Cleavage: The tendency of a mineral to break alongThe tendency of a mineral to break along

smooth, parallel planes. smooth, parallel planes. Due to the presence of weak bonds betweenDue to the presence of weak bonds between

layers of atoms in crystals. layers of atoms in crystals.


When describing cleavage note:When describing cleavage note: The number of cleavage sets;The number of cleavage sets; The angles between the cleavage planes, andThe angles between the cleavage planes, and The developed quality/perfection of each cleavage set.The developed quality/perfection of each cleavage set.

Crystal Form:Crystal Form: Sets of crystal faces define a crystal Sets of crystal faces define a crystal

form, which is a diagnostic property ofform, which is a diagnostic property ofa mineral.a mineral.

Interfacial angles remain constant forInterfacial angles remain constant for any particular mineral. any particular mineral.


Twinning:Twinning: If a crystal lattice alters orientation about a definite plane, the If a crystal lattice alters orientation about a definite plane, the

crystal is said to be crystal is said to be twinned.twinned. May be a highly diagnostic property (i.e. plagioclase felspar, May be a highly diagnostic property (i.e. plagioclase felspar,

and calcite).and calcite).

Specific Gravity:Specific Gravity: The ratio of the weight of a mineral to The ratio of the weight of a mineral to

the weight of an equal volume of water.the weight of an equal volume of water. ““Heft” method of specific gravity estimationHeft” method of specific gravity estimation

used in the field. used in the field.


Other Properties:Other Properties: Effervescence – Effervescence – Reaction to dilute Hydrochloric acid and Reaction to dilute Hydrochloric acid and

release of gas (i.e. Calcite + HClrelease of gas (i.e. Calcite + HCl releases CO releases CO22 gas) . gas) .

Feel/ Touch – Feel/ Touch – Greasy feel like soap (i.e. Talc)Greasy feel like soap (i.e. Talc).. Magnetism –Magnetism – Magnetic attraction or repulsion (i.e. Magnetite, Magnetic attraction or repulsion (i.e. Magnetite,

FeFe33OO44)) . .

These These physical propertiesphysical properties are used to are used to identify rock-forming minerals in hand identify rock-forming minerals in hand specimens and in rocks.specimens and in rocks.

minerals and mineralogy a/prof john m. worden dec university of southern queensland

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