Minerals in Sedimentary Systems II. Evaporates Arabian Gulf Panamint Valley A California Salt Lake California Desert Sands Mediterranean Evaporates Evaporate Deposits Evaporate Minerals Evaporite minerals from seawater Halides, sulfates, carbonates,….while not here borates are also important Evaporite sequence • From seawater, evaporite minerals tend to form in a specific sequence • Calcite • Gypsum • Halite • Mg and K sulfates and chlorides Evaporite sequence • • • • • Evaporate 1000 ft. of seawater to get minor calcite 0.5 ft. of gypsum or anhydrite 11.8 ft. of halite 15 ft. Mg and K sulfates and chlorides including NaCl • Halite (NaCl) often forms 95% of the chloride minerals Halides • • • • • Defined by the dominance of Halogen ions Cl-, Br-, F-, IStrongly ionic Halite, sylvite common evaporates In halite, individual molecules do not exist instead a single crystal lattice is present • Fluorite (CaF2) is also a halide, but not an evaporite Halite NaCl Basic use is nutrition and the preservation of food. The term salary comes from the Latin word for salt. Roman soldiers were paid in pounds of salt, and hence the term, “not worth his or her salt”. A halide mineral, isometric, cubic crystals Trona Trona Halides Trona Halite Trona Salt Dome Structure Bedded halite ductilely flows under the great pressures of deep burial. And, due to its low density, halite rises as diapirs from its deep layers to form salt domes. Truncated layers punctured by the rising salt form perfect oil traps, which like the salt is also rising upward. Gulf Coast Salt Domes Iran Salt Domes and Anticlines Iran Salt Domes and Anticlines Salt Dome Trona Pinnacles Tufa mounds are made of aragonite or calcite precipitated around underwater springs at the base of lakes. Trona Pinnacle Carbonate - Tufa Borax Borates • Over 135 known borate minerals; 4 are most common. • Kernite- Na2B4O6(OH)2*3H2O • Borax- Na2B4O5(OH)4*8H2O • Ulexite- NaCaB5O6(OH)6*5H2O • Colemanite- CaB3O4(OH)3*H2O Borax - an Evaporate Mineral Na2B4O5(OH)4 8H2 O Approx. Density : 1.715 Related minerals include colemanite, kernite, and ulexite Borax Well over a century ago borates – usually the disodium tetraborate decahydrate salt (borax decahydrate*, Na2B4O7.10H2O) - became popular wash-day additives. They were famed, once they became easily and cheaply available, for their gentle but strong cleaning action. Ulexite It’s gypsum, var.satin spar Ulexite (NaCaB5O6(OH)6 . 5 H2O) is a borate mineral famous for its unusual optical properties; it's named for its discoverer, the German chemist G. L. Ulex. Sulfates Gypsum CaSO4-2(H2O) Gypsum a commom sedimentary mineral CaSO4-2(H2O) Uses: plaster, wall board, some cements, fertilizer, paint filler, ornamental stone, etc.. Gypsum is one of the more common minerals in sedimentary environments. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Gypsum Gypsum - a Closer View Varieties of Gypsum Gypsum has several variety names that are widely used in the mineral trade. * "Selenite" is the colorless and transparent variety that shows a pearl like luster and has been described as having a moon like glow. The word selenite comes from the greek for Moon and means moon rock. * Another variety is a compact fiberous aggregate called "satin spar" . This variety has a very satin like look that gives a play of light up and down the fiberous crystals. * A fine grained massive material is called "alabaster" and is an ornamental stone used in fine carvings for centuries, even eons. Anhydrite Anhydrite does not form directly, but is the result of the dewatering of the rock forming mineral Gypsum (CaSO4-2H2O). This loss of water produces a reduction in volume of the rock layer and can cause the formation of caverns as the rock shrinks. Anhydrite Phosphates Apatite Apatite The apatite group is composed of minerals of the general formula Ca5(PO4)3(OH,F,Cl). Apatite occurs as a finegrained sedimentary rock called phosphorite as a direct precipitate from sea water. It is also an accessory mineral in many igneous rocks. Miocene Shark’s Tooth Apatite Structure Apatite - a Different View The main producers of phosphate rock and phosphate fertilizers are the USA, the former USSR, China, Africa (the Maghreb countries, Egypt, Senegal, Togo and South Africa), and the Middle East. Several of these countries are developing countries and the phosphate industry makes an important contribution to their economies. More than 75% of the world's commercially exploited phosphate rock is surface mined. Overall, mineral fertilizers account for approximately 80% of phosphate use, with the balance divided between detergents (12%), animal feeds (5%) and specialty applications (3%), e.g. food grade, metal treatment etc. Apatite Phosphorite Outcrop Phosphate rock is formed in oceans in the form of calcium phosphate, called phosphorite. It is deposited in extensive layers that cover thousands of square miles. In the oceans the phosphorus is precipitated by organisms and sometimes by chemical reaction. The most important use of phosphate rock is in the production of phosphate fertilizers for agriculture. Phosphorite Nodules Microscope View of Phosphorite Phosphorus in Sea Water, South Florida Fertilizer Phosphates and evaporites Barite Rose a concretion of sandstone with barite cement Barite Structure BaSO4 Barite Mine Follow the vein Barite Production World Wide 1930 Mining of Barite - Arkansas Barite Barite (BaSO4), the only commercial source of barium and barium compounds, is a relatively soft, inert mineral with a high SG (Specific Gravity) in the range of 4.2-4.5. Approximately 90% of world production is used as a weighting agent in drilling mud for oil and gas wells where the high SG assists in containing pressures and preventing blowouts. Barite Barite is used as a heavy filler in special paper, rubber, paint and plastics. Its radiation absorbing properties are used in special concretes and in barium meals for medical X-ray examinations. Barium compounds are used in ceramic glazes and to enhance the brilliance and clarity of optical and TV glass.