Sedimentary mineral associations

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The Rock Cycle Sedimentary Processes 2) & 3) Sediments are transported and deposited Products of weathering Primary Minerals Residual Minerals Dissolved Ions Feldspar Clay minerals K+, Ca+2, Na+ Aluminum hydroxide Fe-Mg minerals Limonite Hematite & Mg+2 Quartz Quartz Silica Primary Minerals Solids that Ions that are carried remain in soil away in water Detrital sediments -sediments Chemical & biochemical Types of sediment Detrital – mineral & rock fragments Biochemical – shells made of calcite (CaCO3) by organisms that extract the ions from water Chemical – halite (NaCl) crystals that precipitate from water Detrital sedimentary rocks- classified by grain size differences Conglomerate Breccia Sandstone Shale All these rocks have clastic textures – the rocks are composed of particles (fragments) that are cemented together Detrital sediments are sorted by the processes of transportation and deposition Well sorted Poorly sorted Sands and sandstones can be used to interpret the erosional history of an area and the kinds of rocks that were eroded Wellsorted Poorly sorted “Mature” sediments have little feldspar This means that the sediment was derived from weathered rocks or that the feldspar decomposed during transportation in water The same diagram is used to interpret the provenance (source rocks) of sediments Placer deposit– accumulation of sand or gravel containing minerals that are highly resistant to chemical attack and economically valuable - gold, platinum, ilmenite, rutile, zircon, diamond, garnet, magnetite, corundum, monazite These and other chemically resistant minerals are widely used to indicate the provenance of sediments, e.g kyanite, sillimanite, staurolite indicate that metamorphic rocks were eroded Diamonds indicate kimberlite; gold indicates hydrothermal veins, etc Chemical and biochemical sedimentary rocks Travertine Coquina Limestones – composed of calcite Chalk Deep ocean sediments are mainly fine-grained biochemical sediment called oozes, with some hydrogenous (chemical) and terrigenous (wind or water borne) detrital sediment Calcareous & siliceous ooze Manganese nodules are hydrogenous - they precipitate from deep ocean water when the Mn oxidizes: Mn+2 (dissolved) + O2 + 2e- = MnO2 (pyrolusite) Banded Iron Formations – ancient (>2.5 billion year old) sedimentary deposits of ironbearing minerals These indicate that Earth’s early atmosphere was too poor in oxygen to oxidize iron at the site of weathering Dissolved iron was transported in water: 4Fe+2 (dissolved) + 3O2 = 2Fe2O3 (hematite) Phosphates form in shallow marine environments where dissolved PO 4-3 is carried by upwelling of deep ocean water These areas are biologically productive - many fossils are found, especially bone material Phosphate Mining of the Bone Valley Formation in Florida Evaporite minerals Shallow basin with high rate of evaporation – Gulf of Mexico, Persian Gulf, ancient Mediterranean Sea, Red Sea Sequence is: calcite, gypsum, halite with increasing evaporation Evaporites Seawater evaporation: 1) 2) 3) 4) 5) 6) Gypsum Calcite Gypsum Anhydrite Halite (95% evaporation) Sylvite Other rare minerals Dolomite may form afterward by reaction of Mg+2 with calcite Continental waters: Borax & borates Nitrates Halite Salt dome Sulfur is produced by sulfate reducing bacteria which consume the oxygen in gypsum or anhydrite [...]... are hydrogenous - they precipitate from deep ocean water when the Mn oxidizes: Mn+2 (dissolved) + O2 + 2e- = MnO2 (pyrolusite) Banded Iron Formations – ancient (>2.5 billion year old) sedimentary deposits of ironbearing minerals These indicate that Earth’s early atmosphere was too poor in oxygen to oxidize iron at the site of weathering Dissolved iron was transported in water: 4Fe+2 (dissolved) + 3O2... the Bone Valley Formation in Florida Evaporite minerals Shallow basin with high rate of evaporation – Gulf of Mexico, Persian Gulf, ancient Mediterranean Sea, Red Sea Sequence is: calcite, gypsum, halite with increasing evaporation Evaporites Seawater evaporation: 1) 2) 3) 4) 5) 6) Gypsum Calcite Gypsum Anhydrite Halite (95% evaporation) Sylvite Other rare minerals Dolomite may form afterward by reaction
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