L3: Minerals and Rocks Identification Classification Formation } of common minerals & rocks Feedback on Lab 1: Rock Identification Minerals Definition: Highly-ordered crystalline atomic structure Definite chemical composition (Naturally occuring) homogeneous solid Not minerals: Polymorphs: coal glass diamond (C) graphite (C) Crystallography A vast and hideously complicated subject... 32 crystal classes by symmetry elements: rotation symmetry rotoinversion symmetry mirror symmetry combinations of above Classes grouped into 6 crystal systems: triclinic monoclinic orthorhombic tetragonal hexagonal isometric Met Ig Sed Common Minerals to Learn Olivine (Mg,Fe,Ca) Silicate Pyroxene (Mg,Fe,Ca) Silicate Amphibole (Mg,Fe,Ca) Silicate + OH Feldspar (K,Na,Ca) Al-Silicate Quartz Silica Mica Biotite, Muscovite (K,Mg) Al-Silicate + OH Clay Kaolinite, Montmorillonite Al-Silicate + OH Chlorite (Mg,Fe) Al-Silicate + OH Serpentine Mg Silicate + OH Calcite & Dolomite CaCO3 & (Ca,Mg)CO3 Gypsum Calcium Sulphate + H2O Hematite & Magnetite Iron Oxide Pyrite Iron Sulphide
Identifying Common Minerals 1. Colour Checklist of properties 2. Streak Identifying Minerals: Colour White/Pale GYPSUM KAOLINITE 3. Lustre QUARTZ 4. Transparency 5. Habit CALCITE FELDSPAR MUSCOVITE 6. Cleavage 7. Density 8. Hardness Identifying Minerals: Colour Dark Identifying Minerals: Colour Green SERPENTINE BIOTITE OLIVINE PYROXENE AMPHIBOLE CHLORITE
Identifying Minerals: Streak Hematite Fe2O3 Magnetite Fe3O4 Identifying Minerals: Lustre Dull, Earthy Milky white Glassy FELDSPAR KAOLINITE OLIVINE QUARTZ Irridescent, Pearly Adamantine MUSCOVITE Streak: scratch the mineral on the back of a ceramic tile and note the colour BIOTITE DIAMOND Identifying Minerals: Habit Identifying Minerals: Form Characteristic crystal shape; Related to crystallography Characteristic form of crystals Cubic Laths e.g. Pyrite e.g. Feldspar Sheets Fibrous e.g. Micas e.g. Asbestos Euhedral...... Subhedral..... Anhedral Quartz Olivine Quartz
Identifying Minerals: Cleavage Planes of weakness within crystal lattice Identifying Minerals: Hardness Moh's Scale of Hardness 1. Talc 2. Gypsum GYPSUM 3. Calcite 2.5 Fingernail 3. Copper coin 4. Fluorite 5. Apatite CALCITE 5.5 Pocket knife 6. Orthoclase 7. Quartz 8. Topaz 9. Corundum QUARTZ 10. Diamond Rocks 1. Igneous: Frozen magma 2. Sedimentary: Consolidated sediment grains igneous & metamorphic rocks, plant & animal material, minerals precipitated from water 3. Metamorphic: Igneous or sedimentary rocks altered by heat and pressure Rock Classification 1. Grain Size 2. Mineral Content 3. Texture Generally applies to all 3 groups (ig, sed, met)
Igneous Rocks: Important Types Minerals Name coarse fine Olivine, Pyroxene Peridotite Pyroxene, Feldspar Gabbro (Diorite Granite Mica, Quartz, Feldspar Colour Occurrence Igneous Rocks: Grain Size Grain Size depends on rate of crystal growth Usually reflects depth of crystallisation: Intrusive vs Extrusive Mantle Basalt Andesite) Rhyolite Dark Light Oceanic crust Continental crust Continental crust Gabbro Igneous Rocks: Mantle Peridotite (Olivine + Pyroxene) Xenoliths Basalt Igneous Rocks: Composition Melting of mantle rocks generates magma rich in Mg & Fe ('Mafic') and poor in SiO2 --> Gabbro & Basalt OCEANS Re-melting and melting in presence of water increases SiO2 and decreases Mg, Fe --> Granite & Rhyolite CONTINENTS
Sedimentary Rocks 1. Clastic: Grains (clasts) of silicate minerals Clastic Sed Rocks: Grainsize Grainsize {Clay Silt ~0.01 mm Sand Pebbles Cobbles Boulders Limestones Evaporites Cherts Clastic Sed Rocks: Grainsize few microns Mud 2. Chemical Rock Name 0.1 1 mm ~1cm > 10cm Claystone Siltstone Sandstone } Mudstone } Conglomerate/ Breccia Clastic Sed Rocks: Composition Arenite: Mainly quartz Arkose: Mainly Feldspar Greywacke:Poorly sorted sand & mud Breccia Conglomerate Lithic clast: Piece of rock
Metamorphic Rocks Regional Metamorphism Protolith (original rock type) Type and degree of metamorphism Regional (mountain building temperature and pressure) Contact (heat from igneous rocks) Slate slatey cleavage Schist foliation Gneiss Metamorphoism: Influence of Protolith Limestones -> Marble Sandstones -> Quartzites Mafic Igneous -> Serpentinite