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Show 19 The extent of the bed north and south of the causeway is not known. The mirabilite is interbedded with thin, soft lake- bottom clays. The composition of the deposit and the dissolved solids of the pore water and the theoretical composition of mirabilite are given in Table 3. A seismic survey conducted by Mickulich and Smith ( 1974) may indicate that mirabilite deposits underlie the area generally described by Eardley ( 1962). The deposits are overlain by about 80 feet of Lake sediments, and may be as thick as 700 feet, and underlie an area of about 250 square miles. If these deposits are 80 percent mirabilite, they contain approximately 600 million metric tons of sodium sulfate. The origin of the Lake's mirabilite deposits is uncertain. However, at present, mirabilite precipitates from Great Salt Lake brines during the winter, indicating that they may have formed during an ice age. The Halocene or Recent deposits are about 12 feet thick ( Eardley and Gvasdetsky, 1960). They consist of oolitic sands, algae bioherms, stratified clays and salt ( see Figure 2). Oolites are sperical particles which form by lime accretion on brine shrimp fecal pellets or fragments of rock. On the west shore of Antelope Island, the southwest shore of Promontory Point and on Rozel Point, oolites have become cemented together to form shingle beaches ( Eardley, 1938). The oolitic sands in Great Salt Lake vary in size from 0.15 to 1.5 mm, but the deposits at any given locality consist of relatively uniform- sized oolites. Oolites are composed of two parts-- l) the nucleus, and 2) concentric layers of carbonate minerals, aragonite ( CaC03, orthorombic), calcite ( CaCOo, hexagonal), and dolomite ( CaMg( C03) 2> hexagonal). The |