Graduate Entry MBSS at Imperial Dr Tanya Tierney [email protected].
EARTH MATERIALS IV Rock-forming minerals: non-silicates Professor Peter Doyle [email protected]...
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Transcript of EARTH MATERIALS IV Rock-forming minerals: non-silicates Professor Peter Doyle [email protected]...
EARTH MATERIALS IVEARTH MATERIALS IV
Rock-forming minerals: non-silicatesRock-forming minerals: non-silicates
Professor Peter [email protected]
CLASSIFICATION OF MINERALSCLASSIFICATION OF MINERALS
Mineral class Example
SILICATES Olivine (Mg,Fe)2 SiO4 CARBONATES Calcite CaCO3 SULPHATES Anhydrite CaSO4
OXIDES Hematite Fe2O3
SULPHIDES Pyrite FeS2
HYDROXIDES Brucite Mg(OH)2
HALIDES Halite NaClNATIVE Gold Au
Carbonates• Calcite CaCOCalcite CaCO33 – – trigonaltrigonal
• Aragonite CaCOAragonite CaCO33 – – orthorhombicorthorhombic
• Calcite & Aragonite are polymorphs - same composition, different crystal structure
• Dolomite CaMg (CODolomite CaMg (CO33))22 – trigonal – trigonal
Calcite
Calcite & Aragonite
stable at different
temperatues
CARBONATE MINERALS
CALCITE CaCO3 DOLOMITE CaMg(CO3)2
Ca Ca
Mg
Ca
Mg
Ca
Ca
Carbonates: most commonly found in carbonate most commonly found in carbonate sediments e.g. limestonessediments e.g. limestones
Modern carbonate sedimentsmay contain aragonite &calcite
Ancient carbonates rarely contain aragonite which transforms on burial to calcite
Carbonates in hand specimen
• Vitreous to pearly lustre • Hardness, generally <5 • Trigonal carbonates show perfect
rhombic cleavage• Calcite and aragonite effervesce,
readily soluble in cold dilute HCl• Dolomite only reacts in hot dilute
HCl
Sulphates
• Gypsum CaSO4.2HGypsum CaSO4.2H22O– O– monoclinicmonoclinic
• Anhydrite CaSOAnhydrite CaSO44 – – orthorhombicorthorhombic
• Vitreous to pearly lustre• Hardness <4• Usually occur in evaporite depositsUsually occur in evaporite deposits
Gypsum twin
Twin plane
EVAPORITES IN PLAYA LAKE
EVAPORITES IN MARINE SALINA
Gypsum in hand specimen
• Tabular, fibrous , granular,massive (alabaster) habits
• Often twinned• Soft (H = 2)• One perfect + 2 good cleavages
Gypsum in evaporite deposits
Anhydrite in hand specimen
• H = 3.5• 3 Good/perfect intersecting
cleavages at right angles• Fibrous, granular habits
Nodular anhydrite after gypsum in modern arid tidal flat, ( sabkha )Abu Dhabi, Arabian Gulf
Nodular ‘chicken wire’ anhydrite in Permian sediments, UK
HalidesHalite NaClHalite NaCl• Chloride minerals
characterised by salty taste
• Readily soluble in water• H<3
Fluorite CaFFluorite CaF22
• Well defined cleavage • vitreous lustre • H = 4 • Variable colours - white
streak
HALITE
FLUORITE
Oxides
Hematite FeHematite Fe22OO33 – cubic – cubicMagnetite FeMagnetite Fe22OO44 – cubic – cubic
• Most oxides opaque with metallic lustre• Some transparent with vitreous-resinous lustre• H >5
Botryoidal hematite
Streak - constant
Sulphides
Pyrite FeSPyrite FeS22 – cubic – cubicGalena PbS – cubicGalena PbS – cubicChalcopyrite Cu FeSChalcopyrite Cu FeS22 – cubic – cubic Sphalerite ZnS – cubicSphalerite ZnS – cubic
• Sulphides opaque • metallic lustre• H ≤6
PYRITE
GALENA