Gypsum 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 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 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 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 Psilomelane MnO2 MnO2 Mn O OH 2 Bax Mn4 Mn3 8O16 Kx Mn4 Mn3 8O16 Nax Mn4 Mn3 8O16 Pbx Mn4 Mn3 8O16 Ca Na K X Mn4 Mn3 6O12 3 5H2O LiAl2 Mn2 Mn3 O6 OH 6 ZnMn3O7 3H2O Na Ca Mn7O14 2 8H2O MnO2 nH2O MnOOH MnOOH MnOOH Mn2 Mn23 O4 Mn2O3 Mn OH 2 MnO Wad Al oxides Aluminum occus in economic deposits principally as bauxite Bauxite is a mixture of Al oxides and oxyhydroxides Diaspore AlO OH Gibbsite Al OH 3 B hmite AlO OH Al is a residual phase and bauxite occurs where weathering is extreme and thick layers of aluminum oxyhydroxide are left over Iron Oxides Interaction of dissolved iron with oxygen yields iron oxide and iron oxyhyroxide minerals 1st thing precipitated amorphous or extremely fine grained nanocrystaliine iron oxides called ferrihydrite Fe2 O2 Ferrihydrite Ferrihydrite Fe5O7OH H2O Fe10O15 9H2O some argument about exact formula a mixed valence iron oxide with OH and water Goethite Ferrihydrite recrystallizes into Goethite FeOOH There are other polymorphs of iron oxyhydroxides Lepidocrocite FeOOH Akaganeite FeOOH Iron Oxides Hematite Fe2O3 can form directly or via ferrihydrite goethite hematite Red brown mineral is very common in soils and weathering iron bearing rocks Magnetite Fe3O4 Magnetic mineral of mixed valence must contain both Fe2 and Fe3 how many of each Spinel structure 2 3 of the cation sites are octahedral 1 3 are tetrahedral Banded Iron Formations BIFs HUGE PreCambrian formations composed of hematite jasper chalcedony bands Account for 90 of the world s iron supply Occur only between 1 9 and 3 8 Ga many sites around the world Hammersley in Australia Ishpeming in Michigan Isua in Greenland Carajas in Brazil many other sites around the world BIFs and bacteria Early earth did not have free O2 as microbial activity became widespread and photosynthetic organisms started generating O2 the reduced species previously stable without the O2 oxidized for Fe this results in formation of iron oxide minerals