Minerals barite, BaSO

A second sedimentary component important for paleoceanographic reconstructions, which is prone to dissolution under conditions of sulfate reduction - or more precisely in srrlfate-depleted sediments - is the barium sulfate mineral, barite (BaSO ). Since a correlation has been detected between barite deposition and the flux of organic matter through the water column, the concentration of barite in sediments has been proposed and applied as a geochemical tracer to reconstruct past changes in ocean productivity (e.g.. Bishop... 

Alchemists in the early Middle Ages knew about some barium minerals. Smooth round pebble-like stones found in Bologna, Italy, were known as Bologna stones. When these odd stones were exposed to sunlight, or even a primitive reading lamp, they would continue to glow for several years. This characteristic made them attractive to witches as well as the alchemists. These stones are actually the mineral barite, barium sulfide (BaSO ), which today is a major source of barium metal. 

For comparison with Tables I and II, Table lit gives the range and typical values of the mineral distributions observed in bituminous coals by the CCSEM and Mossbauer techniques, derived from studies of perhaps a hundred different bituminous coal samples in this laboratory. Some obvious differences in mineralogy are apparent. In addition to the difference in calcium dispersion and abundance already noted, it is seen that certain minerals common in bituminous coals, such as Fe-bearing clays (illite and chlorite) and siderite, are virtually absent in the low-rank samples of Tables I and II. Conversely, minerals such as barite (BaSO ), apatite (Ca5(P0 )30H), and other Ca, Sr phosphates are rather uncommon in bituminous coals. 

Besides the precipitation of mineral phases, dissolution of numerous minerals initially supplied to the seafloor can occur in sediments that experience sulfate reduction and/or sulfate-depleted conditions. Iron (oxyhydr)oxides and barite (BaSO ) are two examples with particular relevance for paleoceanographic research. 

Sulfur is a component of numerous minerals. Sulfides include iron pyrite ( fool s gold, FeS ), zinc blende (ZnS), galena (PbS), and cinnabar (HgS). Sulfates include gypsum (CaSO H O) and barite (BaSO ). These ores are among industry s principal sources of copper, zinc, lead. 

The most common sulfate compounds are SrSO, BaSO, and PbSO, which are all white solids. Minerals that contain these compounds include celestite (SrSO ), barite (BaSO ), and anglesite (PbSO ). Minerals that contain calcium sulfate (CaSO ) are relatively common, and... 

Barite, predominately BaSO, meets the overall requirements for weighting material better than other materials and is used for increasing the density of drilling fluids throughout the world. Commercial barite has a lower specific gravity than pure barium sulfate owing to the presence of associated minerals, such as silica. Barite is virtually insoluble in water and does not react with other mud constituents. Most operators prefer barite that meets API specifications (Table 2) (23). The barite content in mud depends on the desired density but can be as high as 2000 kg/km (700 lb/bbl). 

Other inorganic crystals studied by Mark and his collaborators, sometimes leading to complete structure determinations, include strontium chloride, zinc hydroxide, tin tetraiodide, potassium chlorate, potassium permanganage, and ammonium ferrocyanide. Minerals investigated by them include CaSO (anhydrite), BaSO (barite), PbSO, Fe2TiO[j (pseudobrookite), and three forms of Al2Si05 (cyanite, andalusite, and sillimanite). 

Barium is the 17th most abundant element in the Earth s crust, making up about 0.05% of the crust. It is found in the minerals witherite, which is barium carbonate (BaCO ), and barite, known as barium siflfate (BaSO ). Pure barium metal does not exist on Earth—only as compounds or in minerals and ores. Barium ores are found in Missouri, Arkansas, Georgia, Kentucky, Nevada, California, Canada, and Mexico. 

The barium content in the lithosphere is ca. 500 mg/kg (i.e., ppm wt.), but, owing to its chemical reactivity, the metal does not occur free in nature. The chief barium-containing minerals are the sulfate barite or heavy spar [BaSO orthorhombic] and the carbonate with-erite [BaCO, orthorhombic). 

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