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 MnO 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 = –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 goethite- limonite

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