L6. Physical properties of minerals.pdf

Lec 6/ Lab 5: Physical Properties of Minerals Geol 103: Elementary Mineralogy  Color Physical Streak Luster properties Habit Direct result of a mineral’s chemical and structura...

Lec 6/ Lab 5: Physical Properties of Minerals Geol 103: Elementary Mineralogy  Color Physical Streak Luster properties Habit Direct result of a mineral’s chemical and structural Hardness characteristics Cleavage and fracture Other properties Lec 6/ Lab 4: Physical Properties of Minerals  Mineral ID Kit Lec 6/ Lab 4: Physical Properties of Minerals  Color Combination of wavelengths of light incident on the mineral’s surface which reaches the observer’s eyes Lec 6/ Lab 4: Physical Properties of Minerals  Color Combination of wavelengths of light incident on the mineral’s surface which reaches the observer’s eyes Lec 6/ Lab 4: Physical Properties of Minerals  Human eye interpretation of Factors transmitted wavelengths affecting Mineral chemistry Crystal field interaction: presence of a color transition element Charge transfer transitions Color centers due to structural defects Presence of trace elements Lec 6/ Lab 4: Physical Properties of Minerals Emerald (green beryl) due Sapphire (blue corundum) to absorbing ion Cr3+ due to ionic pair Fe2+ and Ti4+ Amethyst (purple quartz) Rose quartz (pink quartz) due to structural defects due to traces of Ti, Fe, or Mn Lec 6/ Lab 4: Physical Properties of Minerals Lec 6/ Lab 4: Physical Properties of Minerals  Mineralogy student Non-mineralogy student Lec 6/ Lab 4: Physical Properties of Minerals Lec 6/ Lab 4: Physical Properties of Minerals Lec 6/ Lab 4: Physical Properties of Minerals Lec 6/ Lab 4: Physical Properties of Minerals Lec 6/ Lab 4: Physical Properties of Minerals  Streak Color of mineral in powdered form Lec 6/ Lab 4: Physical Properties of Minerals  Streak Color of mineral in powdered form Lec 6/ Lab 4: Physical Properties of Minerals  Streak Color of mineral in powdered form Lec 6/ Lab 4: Physical Properties of Minerals  Luster General appearance of a mineral surface in reflected light Lec 6/ Lab 4: Physical Properties of Minerals  Luster General appearance of a mineral surface in reflected light Lec 6/ Lab 4: Physical Properties of Minerals  Luster General appearance of a mineral surface in reflected light Lec 6/ Lab 4: Physical Properties of Minerals  Luster General appearance of a mineral surface in reflected light Lec 6/ Lab 4: Physical Properties of Minerals  Luster General appearance of a mineral surface in reflected light Lec 6/ Lab 4: Physical Properties of Minerals  Luster General appearance of a mineral surface in reflected light Lec 6/ Lab 4: Physical Properties of Minerals  Luster General appearance of a mineral surface in reflected light Lec 6/ Lab 4: Physical Properties of Minerals  Habit Describes the general shape of a crystal Lec 6/ Lab 4: Physical Properties of Minerals  Habit Describes the general shape of a crystal Dendritic Botryoidal Micaceous Bladed Acicular Massive Lec 6/ Lab 4: Physical Properties of Minerals  Habit Describes the general shape of a crystal Lec 6/ Lab 4: Physical Properties of Minerals  Hardness Resistance of a mineral surface to scratching Measurement Method Description Mohs Hardness Comparison of relative hardness of 10 minerals based Relative Scale on the ability of one mineral to scratch another Optical method used for testing of thin layers and Knoop Method brittle materials (best for small, longish test Absolute specimens) Optical method used for testing small, rounded Vickers Method specimens Lec 6/ Lab 4: Physical Properties of Minerals  Hardness Resistance of a mineral surface to scratching HARDNESS MINERAL COMMON OBJECTS HARDNESS MINERAL COMMON OBJECTS 1 Talc 6 Orthoclase Streak plate (6.5) 2 Gypsum Fingernail (2.5) 7 Quartz 3 Calcite Copper (3.5) 8 Topaz 4 Fluorite Nail (4.5) 9 Corundum Steel knife, window 5 Apatite 10 Diamond glass (5.5) Lec 6/ Lab 4: Physical Properties of Minerals  Hardness Resistance of a mineral surface to scratching Knoop Method Vickers Method Lec 6/ Lab 4: Physical Properties of Minerals  When determining a minerals hardness using the Mohs scale, the following should be observed: Hardness 1. Clean the surface before testing Resistance of a mineral 2. Test only on fresh mineral surfaces surface to scratching 3. Habit may affect proper mineral hardness determination 4. It is advisable to scratch both minerals against each other. Lec 6/ Lab 4: Physical Properties of Minerals  Hardness Resistance of a mineral surface to scratching Dependent on the chemical bonds present in the mineral Graphite Diamond Lec 6/ Lab 4: Physical Properties of Minerals  Cleavage and fracture Cleavage Fracture Tendency of mineral to break or Surface of a mineral when it split easily in certain well- does not break along cleavage defined directions planes Lec 6/ Lab 4: Physical Properties of Minerals  Characterized based on 1. Number and pattern of planes Cleavage No. of cleavage planes < possible crystal Tendency of mineral to break faces or split easily in certain well- defined directions 2. Quality of surface and ease of cleaving May be perfect, excellent, good, fair, poor, or none Lec 6/ Lab 4: Physical Properties of Minerals  Cleavage Tendency of mineral to break or split easily in certain well- defined directions Lec 6/ Lab 4: Physical Properties of Minerals  Cleavage Tendency of mineral to break or split easily in certain well- defined directions Sheet/ 1 direction at 1800 Lec 6/ Lab 4: Physical Properties of Minerals  Cleavage Tendency of mineral to break or split easily in certain well- defined directions Prismatic/ 2 directions at 900 Lec 6/ Lab 4: Physical Properties of Minerals  Cleavage Tendency of mineral to break or split easily in certain well- defined directions Cubic/ 3 directions at 900 Lec 6/ Lab 4: Physical Properties of Minerals  Due to: Fracture Bond strength distribution in different Surface of a mineral when directions it does not break along cleavage planes Mineral structure and composition Lec 6/ Lab 4: Physical Properties of Minerals  Fracture Surface of a mineral when it does not break along cleavage planes Conchoidal fracture shows a smooth, curved fracture Lec 6/ Lab 4: Physical Properties of Minerals  Fracture Surface of a mineral when it does not break along cleavage planes Fibrous fracture shows fibers or splinters Lec 6/ Lab 4: Physical Properties of Minerals  Fracture Surface of a mineral when it does not break along cleavage planes Fibrous fracture shows fibers or splinters Lec 6/ Lab 4: Physical Properties of Minerals  Fracture Surface of a mineral when it does not break along cleavage planes Hackly fracture shows jagged with sharp edges Lec 6/ Lab 4: Physical Properties of Minerals  Fracture Surface of a mineral when it does not break along cleavage planes Uneven/ irregular fracture shows rough and irregular surfaces Lec 6/ Lab 4: Physical Properties of Minerals  Other properties Lec 6/ Lab 4: Physical Properties of Minerals  Effervescence Reaction of a carbonate mineral with acid: 2H+ + CO3  H2O + CO2 Lec 6/ Lab 4: Physical Properties of Minerals  Diaphaneity Ability and quality to transmit light Opaque Translucent Transparent Lec 6/ Lab 4: Physical Properties of Minerals  Iridescence Series of colors due to the interference of incident lights at different angles Surface iridescence Internal iridescence Lec 6/ Lab 4: Physical Properties of Minerals  Ferromagnetic: Strongly magnetic Magnetism Paramagnetic: Slightly magnetic Diamagnetic: Not magnetic Lec 6/ Lab 4: Physical Properties of Minerals  Piezoelectricity Mechanical stress cause minerals to acquire an electric charge Lec 6/ Lab 4: Physical Properties of Minerals  Pyroelectricity Temperature changes cause minerals to acquire an electric charge Lec 6/ Lab 4: Physical Properties of Minerals  Smell and taste Due to the chemical elements composed Halite (rock salt) is characterized by its salty taste Lec 6/ Lab 4: Physical Properties of Minerals  Smell and taste Due to the chemical elements composed Sulfur is characterized by its distinct rotten egg smell Lec 6/ Lab 4: Physical Properties of Minerals  Specific gravity Ratio between the density of an object, and a reference substance (usually water) Graphite Diamond Lec 6/ Lab 4: Physical Properties of Minerals  Tenacity Resistance of mineral to breaking, crushing, bending, or tearing Lec 6/ Lab 4: Physical Properties of Minerals  Twin elements 1. Twin plane: reflection by a mirror plane Twinning 2. Twin axis: Rotation about a crystal direction Crystallographically- controlled intergrowths common to both twin with the angular of 2 or more crystals of rotation normally at 180°; the same minerals 3. Twin center: Inversion about a point Lec 6/ Lab 4: Physical Properties of Minerals Twinning Contact twins: definite composition surface Crystallographically- Penetration twins: irregular composition surface controlled intergrowths Polysynthetic twins: repeated twins are parallel of 2 or more crystals of the same minerals Cyclic twins: repeated twins are not parallel Lec 6/ Lab 4: Physical Properties of Minerals  Twinning Crystallographically- controlled intergrowths of 2 or more crystals of the same minerals Contact twins Lec 6/ Lab 4: Physical Properties of Minerals  Twinning Crystallographically- controlled intergrowths of 2 or more crystals of the same minerals Polysynthetic twins Lec 6/ Lab 4: Physical Properties of Minerals  Twinning Crystallographically- controlled intergrowths of 2 or more crystals of the same minerals Cyclic twins Lec 6/ Lab 4: Physical Properties of Minerals  pp. 334- 557 Lec 6/ Lab 4: Physical Properties of Minerals