Physical Properties of Minerals Physical Properties Color of

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 – 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 Mn. O 2 • red color in many minerals is caused by hematite inclusions

• Mineral Properties Related to Light, Heat, and Electricity • Play of Colors (Iridescence) • defracted or reflected light off features on the mineral – labradorite and opal

• 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

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

• sectile--if mineral can be cut into thin shavings--talc • ductile--if mineral can be drawn into wire-Cu, Au • flexable--if a mineral is bent and does not assume its’ original shape • elastic--if a mineral is bent and resumes its’ original shape--mica talc

• 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

talc--pearly

• greasy--like grease or oil--massive quartz • silky--like silk--satin spar gyspum • adamantine--brillant with a high index of refraction--diamond or clear quartz crystals

• 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)

• S. G. can be determined with a Jolly Balance • 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

acicular-stibnite

• 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 radiated--wavellite

• groups of distinct crystals in parallel or spherical form – columnar--column like crystals – bladed--many flat knife like crystals – fibrous--parallel fibers – colloform--botryoidal (bunch of grapes, reniform (kidney shaped), mammillary fibrous--crysotile (serpentine) colloform-hematite

• aggregate of scales or lamellae – foliated--easily splits into thin sheets or leaves – plumose--scaly-feather like • granular aggregate – equant crystal grains foliated (micaceous)- mica equant granular mass- pyrite

• Other types 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 stalactitic-resembling stalactites---this example is goethitelimonite

massive--massive with no form or distinguishing features geode--rock cavity filling with mineral crystals

banded--mineral showing narrow bands of different colors or textures