Mineraloji Physıcal Properties of Minerals PHYSICAL PROPERTIES OF MINERALS PHYSICAL PROPERTIES OF MINERALS useful diagnostic parameters to identify minerals macroscopically important useful in industry e.g. talc softest mineral (skin care) cor hard mineral (abrasive) musc low electrical conductor, good insulator ISOTROPISM LECTURE II isotropic physical properties same in all directions gases, liquids, amorphous and cubic minerals (isometric system) anisotropic physical properties variable with crystallographic directions minerals in tetragonal, orthorhombic, hexagonal, monoclinic and triclinic systems best displayed in optical propertiesPOLYMORPHISM physical properties related to atomic str., bonding forces and chem. composition minerals having same chemical composition with different crystal structure (as a function of changes in P & T or both) crystallization in different Symmetry Systems different physical properties polymorphism minerals polymorphous Dimorphic Trimorphic Polymorphic number of min. species in the groupDimorphic Comp. SG. System Hardness Diamond C3 . 5 1 C u b i c 1 0 Graphite C 2.23 Hex. 1-2 Calcite CaCO 3 2.71 Rhomb. 3 Aragonite CaCO 3 2.95 Ortho. 3.5-4 Trimorphic Andalusite Al 2 SiO 5 3.13-3.16 Orth. 6.5-7.5 Kyanite Al 2 SiO 5 3.53-3.65 Tri. 5.5-7.0 Sillimanite Al 2 SiO 5 3.23-3.27 Orth. 6.5-7.5 PolymorphicComp. SG. System Hardness Low Quartz SiO 2 2.65 Hex. 7 high Quartz SiO 2 2.53 Hex 7 High Tridymite SiO 2 2.26 Mono; Orth. 7 High Cristobalite SiO 2 2.32 Cubic; Tetr. 6.5 Coesite SiO 2 3.01 Mono 7.5 Stishovite SiO 2 4.35 Tetr 7I. Characters Depending upon Cohesion and Elasticity II. Characters Depending upon Specific Gravity III. Characters Depending upon Light IV. Characters Depending upon Magnetism VI. Characters Depending upon CRYSTAL and AGGREGATES HABITS V. Characters Depending upon Senses PHYSICAL PROPERTIES PHYSICAL PROPERTIES I. Characters Depending upon Cohesion and Elasticity Cohesion force of attraction existing btw molecules resistance to any external influence (e.g. breaking or scratching) bonding force Elasticity force tending to restore molecules of a body into their original position cleavage, parting, fracture, hardness and tenacityCLEAVAGE tendency of a crystalline mineral to break in certain directions yielding more or less smooth planar surfaces planes of lowest bond energy min. value of cohesion amorphous body no cleavage cleavage planes usually // to the crystallographic planes cleavage consistent with symmetry cubic octahedral dodecahedral rhombohedral prismatic and pinacoidal basal (pinacoidal)classified according to their distinction and smoothness 1. Good, distinct, perfect 2. Fair, indistinct, imperfect 3. Poor, in traces, difficult related to the atomic structure in several directions depending on the force of cohesion some more developed than the others compared with other atomic planes, distance btw cleavage planes must be large › electrical forces small › cohesion less cleavage planes pearly luster due to partial separation of crystal into parallel plates and reflection of light from these plates PARTING subjected to external force breaks along planes of structural weakness due to pressure, twinning, exsolution resembles cleavage but not continuous on crystals basal parting rhombohedral parting Cleavage fragments of fluorite Cleavage fragments of muscovitekinds of fractures Conchoidal: smooth fracture (Qua,glass ) Fibrous and splintery: sharp pointed fibers (Asbestos, Serpentine) Uneven or irregular: rough and irregular surfaces Even: more or less smooth surfaces, may resemble cleavage Hackly: jagged fractures with very sharp edges (Mat) FRACTURE strength of the bonds approximately same in all directions some crystals structures and amorphous solids irregular surfacesHARDNESS resistance to scratching hardness (H) "scratchability" related to attraction force btw atoms degree of H determined by observing comparatively relative ease or difficulty with which one mineral scratched by another, or by a finger nail, file or knife Mohs scale of hardness relative scale series of 10 common minerals by Austrian mineralogist F. Mohs (1824)1. Talc 2. Gypsum Finger nail >2 3. Calcite 4. Fluorite 5. Apatite Knife >5 Window glass 5½ 6. Orthoclase File 6½ 7. Quartz 8. Topaz 9. Corundum 10. Diamond #1 Talc #2 Gypsum #3 Calcite #6 Orthoclase #4 Fluorite #5 Apatite #7 Quartz #8 Topaz #9 Corundum #10 Diamondoxides and silicates › hard › more than 6 (few exceptions, e.g. Talc) relation btw H and chemical composition very characteristic and useful in identification of minerals in hand specimens native Minerals (Au, Ag, Cu) › soft › max. 3 sulphides › mostly soft › max. 4 (exceptions › minerals with Fe, Co, Ni) carbonates, sulphates and phosphates › soft › max. 5 most hydrated minerals › soft › max. 5 TENACITY resistance to breaking, crushing, bending, cutting, drawing or tearing cohesion brittle breaks and powders easily (Sulfides, Carbonates, Silicates and Oxides) malleable hammered out without breaking into thin sheets plastic (native metals sectile cut with a knife into thin shavings (native metals) ductile drawn into wire (native metals) flexible bends but retains it bent form not resume its original shape › permanent deformation (Asb, clay minerals, Chl, Tal) elastic after bending springs back and resumes its original position (Mus)II. Characters Depending upon Specific Gravity Specific gravity (SG) relative density unitless number ratio btw weight of substance and weight of equal volume of water at 4 (Max. ). Density weight of a substance per volume= g/cm 3 variable from one locality to another (max. at poles, min. at equator) SG measure with a simple balance weighing specimen + in air (w a ) in water (w w ) SG=w a /(w a -w w ) volume of substance specimen clean free air bubbles cavitiesr relation between SG and other physical and chemical properties elation between SG and other physical and chemical properties minerals with non-metallic luster SG ave 2.6-3.0 Qua=2.65, Felds = 2.60-2.75 hydrated and soft minerals SG<2.6 hard mins with heavy elements (Sr, Ba, Fe, W, Cu, Ag, Pb, Hg) SG>3.5 minerals with metallic luster SG>5 Pyt=5, Gal=7.5, Mat=5.18 in isostructural compounds, those with heavy element higher SG Mineral Composition Atomic Wt. SG Aragonite CaCO3 40.08 2.94 Strontianite SrCO3 87.62 3.78 Witherite BaCO3 137.34 4.31 Cerussite PbCO3 207.19 6.58 in solid solution series continuous change in SG with change in chem. comp. Fos=3.3 Fay=4.4 in polymorphous compounds closest atomic packing higher SG Grap=2.23 Dia=3.5III. Characters Depending upon Light DIAPHENEITY amount of light transmitted or absorbed by a solid used strictly for hand specimens most minerals opaque in hand specimens transparent in thin sections Transparent object behind it seen clearly Qua, Flu size of specimen Translucent light transmitted but object not seen onyx marble Opaque light wholly absorbed Mat, HemCOLOUR wavelength of the visible light region reflected or transmitted from the mineral human eye sensitive btw 4200-7500 Å observed in white light mineral monochromatic light change in colour of mineral interaction of electromagnetic radiation with a material energies correspond exactly to the energy difference btw electronic levels of atom SO electrons being excited from one level to another not absorbed interfere on each other colour of mineral in ionically bonded crystals next energy level of unoccupied orbital >> energy of visible light no absorption white or colourless impurities cause of colourFeldspar --- Green, Pink White, Gray, Etc. Colorless Gypsum Malachite Turquoise Fluorite AmethystSTREAK colour of mineral powder colour variable but streak usually constant by rubbing a mineral on a hard (H=7), white, unglazed porcelain e.g. hem colour dark steel-gray or iron black streak reddish brown to cherry-redLUSTER general appearance of a mineral surface in reflected light degree of reflected light directly related to optical properties (mainly refractive index: RI) other surface conditions metallic luster strictly opaques light is completely reflected from the surface non-metallic luster most of ore minerals with high content of metals imperfect metallic, sub-metallic other luster types poor reflection (scattered light from min. surface) Related to RI Adamantine exceptionally brilliant luster high RI e.g. Dia, Zir, Cor Vitreous broken glass e.g. Silicates (Qua), Carbonates (Cal)Related to special mechanical and chemical properties of mineral surfaces Resinous Greasy (yellow) resins e.g. Sphalerite, S oily glass due to light scattered by a microscopically rough surface e.g. Nep, massive Qua Pearly pearl-like due to reflection from successive layers (e.g. surfaces parallel to cleavage) e.g. Talc, Mica minerals Silky silk-like due to reflection from fibrous structure of minerals Gyp, Asb, Malachite Earthy little or no reflection from surface due to the porous and fine- grained nature of mineral e.g. limMetallic Luster Adamantine Luster Resinous Luster Vitreous Luster Greasy Luster Earthy Luster Pearly Luster Silky LusterIV. Characters Depending Upon Magnetism Magnetism basic cause of magnetism orbital and spin motions of electrons wth electric field of an atom charged particle in motion creates magnetic moment spin and orbital motion of electrons produce magnetism SO Diamagnetism opposing spins (‘up’ and ‘down’) of two electrons in the same orbital of an atom zero net magnetic moment no attraction for a magnet, in fact they are slightly repelled by a magnetic field e.g. Cal, Alb, Qua, Apa etc. Ferromagnetism magnetic moments // to each other wth grains metallic Fe btw grains randomly arranged when placed in a magnetic field all the domains of all grains will be aligned parallel to the external magnetic fieldFerrimagnetism ionic spin moments anti-parallel magnetic moment of some of the neighbouring atoms SO align themselves in opposite direction cancel each other become permanent magnets eg., Mat Fe 3 O 4 -Ulvospinel Fe 2 TiO 4 permanent magnetism of ferrimagnetic minerals study of ancient geomagnetic fields of earth paleomagnetism ferromagnetic mineral (e.g. Mat) crystallizes from magma assumes magnetic field of Earth at crystallization place position of the continents during geological timeV. Characters Depending Upon Senses TASTE most minerals no taste Asterigent taste of vitriol HCl Saline taste of salt halite NaCl Alkaline taste of soda NaCO 3 Cooling taste of saltpeter or Niter KNO 3 Bitter taste of Epsomsalt MgSO 4 .7H 2 O Sticky taste of clay minerals ODOUR most minerals no odour Garlic minerals with As Horseradish when heated, minerals with Se Bituminous asfaltite, petroleum products Sulphurous when heated, minerals with S Fetid smell of rotten eggs minerals with S, when heated H 2 S evolves Argillaceous moistened clay mineralsFEEL Smooth Sepiolite Greasy Talc Harsh rough surface and harsh feel Cold Corundum Al 2 O 3 Sticky feel to the tongue Clay minerals Heavy high SG Gal CRYSTAL HABITS and AGGREGATES CRYSTAL HABITS and AGGREGATES special terms for habit or general form or appearance of single crystals, crystals grow together in aggregates Isolated or distinct crystals Groups of distinct crystals Parallel or radiating groups of individual crystals Aggregate composed of scales or lamellae Aggregate composed of equant grains MiscellaneousIsolated or distinct crystals Isolated or distinct crystals Acicular slender, needle-like Rut Capillary and filiform hair-like or thread-like Sid Bladed elongated, flattened knife-like KyaSOME SYMMETRY EXAMPLES ISOMETRIC DIAMOND TETRAGONAL WULFENITE HEXAGONAL BERYL TRIGONAL QUARTZ variety - AMETHYST ORTHORHOMBIC TANZANITE MONOCLINIC GYPSUM TRICLINIC MONTEBRASITE AMORPHOUS AMBER Groups of distinct crystals Groups of distinct crystals Dendritic and arborescent slender divergent branches, plant-like native Cu, Ag, Au Reticulated lattice-like slender crystals Divergent or radiatedDrusy surface covered with a layer of small crystals Parallel or radiating groups of individual crystals Parallel or radiating groups of individual crystals Columnar stout, column-like Qua Bladed aggregate of flattened blades Stibnite Fibrous aggregate of slender fibers, radiating or parallel RutColloform Stellated radiating individuals forming star-like, circular groups Globular radiating individuals forming small spherical or hemispherical groups Hem Botryoidal same as globular, resembling bunch of grapes, Hem Reniform same as globular, but in kidney shaped masses Mammillary same as globular, but in mammae shaped masses same as globular › mammillary, AgateAggregate composed of scales or lamellae Aggregate composed of scales or lamellae Foliated thin plates and leaves Micaceous same as foliated but splits into exceedingly thin sheets Micas Lamellar or tabular flat, plate-like Plumose fine scales, with divergent or feather-like structure A Aggregate ggregate composed of composed of equant equant grains grains Granular equal sized anhedral grains (fine, medium or coarse) MassiveMiscellaneous Miscellaneous Stalagtitic successive layer in cylinder or cone shapes. Cal Concentric spherical layers around a common centre Pisolitic rounded masses about pea-sized Oölitic same as pisolitic about fish roe sized Banded narrow band of different texture and colour, Chromite Amygdaloidal almond shaped, Zeolite minerals, Cal filling vesicles in basaltGeode a rock cavity wholly or partly filled with same or different minerals banded or with crystals projecting from walls, Agate Concretion deposition around a nucleus, spherical or irregular shapes Nodular as nodules