Post on 16-Dec-2015
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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
• Mineral Properties Related to Light, Heat, and Electricity• Play of Colors (Iridescence)
• defracted or reflected light off features on the mineral
– labradorite and opal
• 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
• 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
• 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
• 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)- micaequant granular mass- pyrite
• Other typespisolitic 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 goethite-limonite
massive--massive with no form or distinguishing features
geode--rock cavity filling with mineral crystals