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EARTH MATERIALS IV Rock-forming minerals: non-silicates Professor Peter Doyle

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Presentation on theme: "EARTH MATERIALS IV Rock-forming minerals: non-silicates Professor Peter Doyle"— Presentation transcript:

1 EARTH MATERIALS IV Rock-forming minerals: non-silicates Professor Peter Doyle

2 CLASSIFICATION OF MINERALS Mineral classExample SILICATES Olivine (Mg,Fe) 2 SiO 4 CARBONATES Calcite CaCO 3 SULPHATES Anhydrite CaSO 4 OXIDES Hematite Fe 2 O 3 SULPHIDES Pyrite FeS 2 HYDROXIDES Brucite Mg(OH) 2 HALIDES Halite NaCl NATIVE Gold Au

3 Carbonates Calcite CaCO 3 – trigonalCalcite CaCO 3 – trigonal Aragonite CaCO 3 – orthorhombicAragonite CaCO 3 – orthorhombic Calcite & Aragonite are polymorphs - same composition, different crystal structure Dolomite CaMg (CO 3 ) 2 – trigonalDolomite CaMg (CO 3 ) 2 – trigonal Calcite Calcite & Aragonite stable at different temperatues

4 CARBONATE MINERALS CALCITE CaCO 3 DOLOMITE CaMg(CO 3 ) 2 Ca Mg Ca Mg Ca

5 most commonly found in carbonate sediments e.g. limestones Carbonates: most commonly found in carbonate sediments e.g. limestones Modern carbonate sediments may contain aragonite & calcite Ancient carbonates rarely contain aragonite which transforms on burial to calcite

6 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

7 Sulphates Gypsum CaSO4.2H 2 O– monoclinicGypsum CaSO4.2H 2 O– monoclinic Anhydrite CaSO 4 – orthorhombicAnhydrite CaSO 4 – orthorhombic Vitreous to pearly lustre Hardness <4 Usually occur in evaporite depositsUsually occur in evaporite deposits Gypsum twin Twin plane

8 EVAPORITES IN PLAYA LAKE EVAPORITES IN MARINE SALINA

9 Gypsum in hand specimen Tabular, fibrous, granular,massive (alabaster) habits Often twinned Soft (H = 2) One perfect + 2 good cleavages Gypsum in evaporite deposits

10 Anhydrite in hand specimen H = 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

11 Halides Halite NaCl Chloride minerals characterised by salty taste Readily soluble in water H<3 Fluorite CaF 2 Well defined cleavage vitreous lustre H = 4 Variable colours - white streak HALITE FLUORITE

12 Oxides Hematite Fe 2 O 3 – cubic Magnetite Fe 2 O 4 – cubic Most oxides opaque with metallic lustre Some transparent with vitreous-resinous lustre H >5 Botryoidal hematite Streak - constant

13 Sulphides Pyrite FeS 2 – cubic Galena PbS – cubic Chalcopyrite Cu FeS 2 – cubic Sphalerite ZnS – cubic Sulphides opaque metallic lustre H ≤6 PYRITE GALENA


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