Physical properties of minerals
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Physical Properties of Minerals - PowerPoint PPT Presentation

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Physical Properties of Minerals. Physical Properties. Color of Minerals Idiochromatic color color caused by elements in chemical formula--Cu in malachite and azurite and Mn in rhodochrosite. Chromaphore color

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Physical properties
Physical Properties

  • Color of Minerals

    • Idiochromatic color

      • color caused by elements in chemical formula--Cu in malachite and azurite and Mn in rhodochrosite

  • Chromaphore color

    • color caused by concentrations of elements not part of chemical formula--Cu and V in beryl (emerald), Fe in amethyst and V in zoisite (tanzanite)

  • Electron and Molecular Transitions

    • Colors caused by Idiochromatic and chromophore elements can be generated by

      • 1. Crystal field transitions

        • wavelengths of light are absorbed by “d” electrons in transition elements causing emissions of wavelengths of light quanta resulting in color of mineral---Cr+3 in emerald and ruby, Mn+2 in morganite and Fe+2 in peridot

  • 2. Molecular Orbital Transitions

    • ions undergo charge transitions or electron hopping--Fe+2 to Fe+3 in aquamarine or Fe+2 to Ti+4 in sapphire

  • Inclusions of Other Minerals

    • minerals dispersed or included in minerals can influence color

      • chlorite dispersed in quartz (aventurine) can cause a green color

      • black calcite can be caused by inclusions of MnO2

      • red color in many minerals is caused by hematite inclusions

  • Chatoyancy

    • silky or wavey appearance across the surface of the mineral as it is rotated--

  • Asterism

    • a star like figure on surface of mineral caused by reflected or scattered light off included minerals aligned parallel to crystallographic axes

  • Luminescence

    • caused by impurities (activators) in a mineral--some specimens of fluorite, scheelite, and calcite

  • Fluorescence

    • emission of wavelengths of light caused by electron excitation in metals during bombardment by ultraviolet or X-rays

  • Phosphorescence

    • continuous emission of wavelengths after excitation source is removed

  • Thermoluminescence

    • emissions of wavelengths when subjected to heat at less than “red hot” temperatures

    • Piezoelectricity

      • a flow of electrons in minerals with exertion of a compression force between the “c” crystallographic axis of a mineral which has no center of symmetry---quartz and tourmaline

    • Pyroelectricity

      • the same as above brought about by stimulation of mineral with heat--quartz and tourmaline

    • Hardness

      • Moh’s hardness scale is a special list of minerals with increasing relative hardness

        • 1. talc 6. feldspar

        • 2. gypsum 7. quartz

        • 3. calcite 8. topaz

        • 4. fluorite 9. corundum

        • 5. apatite 10. diamond

          • glass and knife = 5.5 - 6

          • steel file = 6 -7

          • fingernail = 2.5

          • penny = 3

          • some minerals have more than 1 hardness depending on the direction of scratching--kyanite= 5-7 and calcite between 2 and 3

    • Tenacity

      • cohesiveness of mineral or resistance to breaking, crushing, bending, etc.

        • 1. brittle--if a mineral powders easily--quartz

        • 2. malleable--if mineral can be hammered into sheets--native Cu, Au


    • Streak and Luster

      • streak is the color of the powder of the mineral on a porcelain plate

      • luster is metallic (dark or black prominent streak--dense and opaque to light) or nonmetallic ( translucent or transparent with a colorless or white streak) or somewhat inbetween called submetallic

        • some specific nonmetallic lusters are:

          • 1.vitreous--resembling glass--quartz crystals

          • 2. resinous--resin like--sulfur and sphalerite

          • 3. pearly--mother of pearl like--talc

    • Cleavage

      • ability of mineral to come apart in a consistent way

      • breakage is along atomic planes--consistent with crystal symmetry--- there can be from one to multidirectional cleavage from mineral to mineral

    • Parting

      • can resemble cleavage

      • breakage of minerals along planes of weakness such as twinning planes--minerals which grow around each other, each one forming at a different time

      • caused by minerals being subjected to special pressures during formation

    • Fracture

      • inability of a mineral to break in a consistent way

      • do not break along cleavage planes

    • Kinds of fracture are:

      • concoidal--smooth, curved breakage--quartz

      • fibrous or splintery

      • hackly--jagged with sharp edges

      • irregular--rough surfaces

  • Specific Gravity

    • a number expressing a ratio between a mineral and the weight of an equal volume of water

    • same number as density without units

    • S.G. depends on:

      • kinds of atoms (atomic weight) comprising mineral

      • packing of atoms(close or loosely packed)

  • Crystal Habits and Aggregates

    • appearance of a single crystal or aggregate of a crystals of a mineral

      • isolated individual crystals

        • bladed--elongated flattened crystal like a knife blade

        • acicular--thin needlelike crystal

        • capillary--hair like or thinner

    • groups of distinct crystals

      • dendritic--resembling a branching tree or veinlets on a tree leaf

      • radiated--crystal appearing in a radial pattern

      • drusy--a surface containing very small crystals


    fibrous--crysotile (serpentine)


    equant granular mass- pyrite

    foliated (micaceous)- mica

    pisolitic or oolitic--rounded masses of pea sized grains (pisolitic) or very small grains( oolitic)---this picture is bauxite (pisolitic) and some samples of hematite occur as oolitic

    • Other types

    stalactitic--resembling stalactites---this example is goethite-limonite

    massive--massive with no form or distinguishing features (pisolitic) or very small grains( oolitic)---this picture is bauxite (pisolitic) and some samples of hematite occur as oolitic

    geode--rock cavity filling with mineral crystals