Major Clay Minerals Kaolinite Al2Si2O5 OH 4 Illite K1 1 5Al4 Si Al 8O20 OH 4 Smectites Montmorillonite Ca Na 0 20 4 Al Mg Fe 2 Si Al 4O10 OH 2 nH2O Vermicullite Ca Mg 0 30 4 Al Mg Fe 3 Si Al 4O10 OH 2 nH2O Swelling clays can take up extra water in their interlayers and are the major components of bentonite NOT a mineral but a mix of different clay minerals Phyllosilicates SiO4 tetrahedra polymerized into 2 D sheets Si2O5 Apical O s are unpolymerized and are bonded to other constituents Phyllosilicates Tetrahedral layers are bonded to octahedral layers OH pairs are located in center of T rings where no apical O Phyllosilicates Octahedral layers can be understood by analogy with hydroxides Brucite Mg OH 2 c Layers of octahedral Mg in coordination with OH Large spacing along c due to weak van der waals bonds Phyllosilicates a2 a1 Gibbsite Al OH 3 Layers of octahedral Al in coordination with OH Al3 means that only 2 3 of the VI sites may be occupied for charge balance reasons Brucite type layers may be called trioctahedral and gibbsite type dioctahedral Phyllosilicates Yellow OH Kaolinite Al2 Si2O5 OH 4 T layers and diocathedral Al3 layers OH at center of T rings and fill base of VI layer weak van der Waals bonds between T O groups T O T O T O vdw vdw Phyllosilicates Yellow OH Serpentine Mg3 Si2O5 OH 4 T layers and triocathedral Mg2 layers OH at center of T rings and fill base of VI layer weak van der Waals bonds between T O groups T O T O T O vdw vdw Clay building blocks Kaolinite micelles attached with H bonds many H bonds aggregately strong do not expend or swell 1 1 Clay Clay building blocks Slightly different way to deal with charge on the octahedral layer put an opposite tetrahedral sheet on it Now how can we put these building blocks together 2 1 Clay Calcite vs Dolomite dolomite less reactive with HCl calcite has lower indices of refraction calcite more commonly twinned dolomite more commonly euhedral calcite commonly colourless dolomite may be cloudy or stained by iron oxide Mg spectroscopic techniques Different symmetry cleavage same but easily distinguished by XRD Calcite Group Variety of minerals varying by cation Ca Calcite Fe Siderite Mn Rhodochrosite Zn Smithsonite Mg Magnesite Dolomite Group Similar structure to calcite but Ca ions are in alternating layers from Mg Fe Mn Zn Ca Mg Fe Mn Zn CO3 2 Ca Dolomite Fe Ankerite Mn Kutnahorite Aragonite Group Polymorph of calcite but the structure can incorporate some other larger metals more easily Pb Ba Sr Ca Aragonite Pb cerrusite Sr Strontianite Ba Witherite Aragonite LESS stable than calcite but common in biological material shells Carbonate Minerals Calcite Group hexagonal Dolomite Group hexagonal AragoniteGroup orthorhombic mineral formula mineral formula mineral Calcite CaCO3 Dolomite CaMg CO3 2 Aragonite CaCO3 Magnesite MgCO3 Ankerite Ca Mg Fe CO3 2 BaCO3 Siderite FeCO3 Kutnohorite CaMn CO3 2 Strontianite Rhodochrosi MnCO 3 te Witherite formula SrCO3 Carbonate Minerals Ca Calcite CaCO3 Dolomite CaMg CO3 2 Magnesite MgCO3 Mg Ankerite CaFe CO3 2 Siderite FeCO3 Fe Sulfate Minerals More than 100 different minerals separated into hydrous with H2O or anhydrous without H2O groups Gypsum CaSO4 2H2O and anhydrite CaSO4 are the most common of the sulfate minerals Gypsum typically forms in evaporitic basins a polymorph of anhydrite CaSO4 forms when the gypsum is later dehydrated Gypsum Gypsum formation can demarcate ancient seas that dried up such as the inland seas of the Michigan basin or tell us about the history of current seas which have dried up before such as the Mediterranean Sea Halide Minerals Minerals contianing halogen elements as dominant anion Cl or F typically Halite NaCl and Sylvite KCl form in VERY concentrated evaporitic waters they are extremely soluble in water indicate more complete evaporation than does gypsum Fluorite CaF2 more typically occurs in veins associated with hydrothermal waters F in hydrothermal solutions is typically much higher leached out of parent minerals such as biotites pyroxenes hornblendes or apatite Halite Structure NaCl Na gray arranged in CCP with Cl red at edges and center in octahedral cavities Flourite structure CaF2 Ca2 gray arranged in CCP Fions red inside cage Sulfate Minerals II Barite BaSO4 Celestite SrSO4 and Anglesite PbSO4 are also important in mining These minerals are DENSE Barite 4 5 Anglesite 6 3 feldspars are 2 5 Barite Celestite Anglesite Metals bond with sulfate much more easily and thus are generally more insoluble they do not require formation in evaporitic basins What do they indicate then Ba Pb Sr very low SO4 2 Lots of SO42Not very much Ba Sr Pb Just silica Chert extremely fine grained quartz Forms as nodules in limestone recrystallization of siliceous fossils Jasper variety with hematite inclusions red Flint variety containing organic matter darker color Chalcedony microcrystaliine silica very similar to low quartz but different it is yet uncertain how different typically shows banding often colored to form an agate rock formed of multiple bands of colored chalcedony Jasper variety colored with inclusion of microcrystsalline oxides often iron oxides red Opal a hydrogel a solid solution of water in silica forms initially as water silica colloids then slowly the water diffuses into the silica making it amorphous no XRD pattern Some evidence opal slowly recrystallizes to chalcedony Opal Gemstone Agates Oxides Oxyhydroxides FeOOH minerals Goethite or Limonite FeOOH important alteration products of weathering Fe bearing minerals Hematite Fe2O3 primary iron oxide in Banded Iron Formations Boehmite AlOOH primary mineral in bauxite ores principle Al ore which forms in tropical soils Mn oxides form Mn nodules in the oceans estimated they cover 10 30 of the deep Pacific floor Many other oxides important in metamorphic rocks Mn oxides oxyhydroxides Mn exists as 2 3 and 4 oxide minerals are varied complex and hard to ID Wad soft i e blackens your fingers brown black fine grained Mn oxides Psilomelane hard does not blacked fingers grayblack botroyoidal massive Mn oxides XRD analyses do not easily distinguish different minerals must combine with TEM SEM IR spectroscopy and microprobe work Mn Oxide minerals not all Romanechite Pyrolusite Ramsdellite Nsutite Hollandite Cryptomelane Manjiroite Coronadite Todorokite Lithiophorite Chalcophanite Birnessite Vernadite Manganite Groutite Feitknechtite Hausmannite Bixbyite Pyrochroite Manganosite Ba 66 Mn4 Mn3 5O10 1 34H2O