The sphere is 6 ft in diameter the pilot and 2 observers sit in that space 1 5 2 hours going down 1 5 2 hours coming up bottom time usually limited by battery consumption Wand nicknamed Fat Albert contains 2 electrodes and a thermistor Voltammetry at 7 500 ft depth Riftia field chemistry Scans up to 20 C little no Fe2 FeS aq few mM HS Black Smoker chemistry Scans up to 220 C lots of Fe2 HS FeS aq tens to hundreds of millimolar Fe and S Sulfides are reduced minerals what happens when they contact O2 This is the basis for supergene enrichment and acidic mine drainage Actively Oxidizing Pyrite FeS2 3 5 O2 H2O Fe2 2 SO42 2 H FeS2 14 Fe3 8 H2O 15 Fe2 2 SO42 16 H 14Fe2 3 5 O2 14H 14 Fe3 7 H2O Sulfur species and H generation FeS2 2 Fe3 3 Fe2 S8 0 H FeS2 7 Fe3 3 H2O 8 Fe2 0 5 S4O62 6 H AMD neutralization Metals are soluble in low pH solutions can get 100 s of grams of metal into a liter of very acidic solution HOWEVER eventually that solution will get neutralized reaction with other rocks CO2 in the atmosphere etc and the metals are not so soluble but oxidized S sulfate SO42 is very soluble A different kind of mineral is formed 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 Gibbsite Al OH 3 common Al oxide forming in aqueous sysems 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 Al oxides Aluminum occurs 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 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 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 Other important oxides Periclase MgO Met mineral from dolomite Brucite Mg OH 2 weathering product Rutile Anatase brooksite TiO2 polymorphs Corundum Al2O3 sapphire and ruby Ilmenite FeTiO3 common in igneous met rx Cuprite Malachite Azurite copper oxides Uraninite UO2 important U ore Spinel MgAl2O4 High P met mineral
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