Pyritized fossils

Figure 6. Grayscale wavelength-dispersive electron microprobe map of arsenic distribution in a segment of a pyritized fossil fragment, LP-l core, 81.2 meters. Arsenic-rich pyrite occurs as overgrowths (bright bands) onframboids (darker spheres). Arsenic contents of the points shown are as follows I 6.6 wt. % 2 7.2 wt. % 3 6.9 wt.% 4 6.7 wt. % 5 6.8 wt. % 6 8.5 wt. % 7 2.0 wt. % 8 1.0 wt. %. Area shown is approximately 400 x 450 0.50 pm pixels.

Many mineral species are known to be selectively crystallized by the presence of bacteria. Carbonate minerals, such as calcite, aragonite, hydroxycalcite, and siderite oxide minerals, such as magnetite and todorokite oxalate minerals, such as whewellite and weddellite sulfide minerals, such as pyrite, sphalerite, wurtzite, greigite, and mackinawite and other minerals, such as jarosite, iron-jarosite, and g3q>sum, are known to precipitate in the presence of bacteria. Therefore, investigations have been developed to analyze the formation of banded iron ore by the action of bacteria, and to analyze the ancient environmental conditions of the Earth through the study of fossilized bacteria. 

Peter Zubovic. The coal is overlain by a black shale sequence which, in places, contains abundant pyritized marine fossils. Above the black shale there generally is a gray shale sequence. The thickness of the two units varies from place to place. The total thickness ranges from about 3-50 feet. I do not know the mineralogy of the shale. I suspect that there is a relation between the total thickness of the shale and the vanadium content of the coal. Parts of this area are being mapped at present, and in the near future we expect to have the data necessary to show if this suggested relation is valid. 

When sulfide ores (such as pyrite), sulfur-rich organic compounds, and fossil fuels (such as coal) are burned in air, the sulfur therein is mostly converted to SO2. 

Frequently fossils are found, particularly in London Clay, consisting of pyrites, the decaying organism having presumably reduced sulphates of iron present in the infiltrating waters. 

To sum up our native fossile Cadmia is our Cobalt, with its several species. But the best manufactured Cadmia is made in furnaces from pyrites, that is marcasite in other words, it is simply made from copper, as Dioscorides teaches. But its name varies with the place where it is manufactured, and with its form and its colour. 

Canfield D. E. and Raiswell R. (1991) Pyrite formation and fossil preservation. In Taphonomy Releasing the Data Locked in the Fossil Record. Topics in Geobiology 9 (eds. P. A. Allison and D. E. G. Briggs). Plenum, New York, pp. 411-453. 

Dill H. G., PoIImann H., Bosecker K., Hahn L., and Mwiya S. (2002) Supergene mineralization in mining residues of the Matchless cupreous pyrite deposit (Namibia)— a clue to the origin of modern and fossil duricrusts in semiarid climates. J. Geochem. Explor. 75, 43-70. 

It is found in non-elemental form in sulfates (gypsum), in sulfidic ores (e.g. iron pyrites and copper, zinc, lead, nickel and cobalt sulfides) and in fossil fuels. In natural gas and crude oil it occurs bonded to both hydrogen and carbon and... 

Such a concretion (shown in thin section in Fig. 3.1.10 and bisected as in Fig. 3.1.11) is believed to have existed initially as an organic gel in a quiet muddy marine sediment. The entrapment of a crab in such a slimy mess is believed to be coincidental, because a fossil crab is not always present (Stenzel, 1934). The irregular fractures are believed to represent subsequent shrinkage [desiccation ( )] cracks which are now partially filled with pyrite, suggesting initial anaerobic petrification. More or less contemporaneously with fracturing, the phosphatization supposedly took place. 

Fig. 3.1.10. Phosphatic concretion from Brazos County, Texas. The large dark object is an appendage of a fossil crab, the tip of which is truncated by a calcite vein. The matrix material is essentially collophane (isotropic francolite), but contains glauconite, quartz, limonite, pyrite, gypsum, etc. in addition to fossil fragments. Magnification 27x. Reproduced with permission (McConnell, 1950).

World sulfur reserves. The earth s crust contains about 0.6% S, where it occurs as elemental S (brimstone) in deposits associated with gypsum and calcite combined S in metal sulfide ores and mineral sulfates as a contaminant in natural gas and crude oils as pyritic and organic compounds in coal and as organic compounds in tar sands (Tisdale and Nelson, 1966). The elemental form commonly occurs near active or extinct volcanoes, or in association with hot mineral spings. Estimates by Holser and Kaplan (1966) of the terrestrial reservoirs of S suggest that about 50% of crustal S is present in relatively mobile reservoirs such as sea water, evaporites, and sediments. The chief deposits of S in the form of brimstone and pyrites are in Western European countries, particularly in France, Spain, Poland, Japan, Russia, U.S.A., Canada, and Mexico. World production of S in the form of brimstone and pyrites was approximately 41 Tg in 1973 other sources accounted for about 8 Tg, making a total of 49 Tg (Anon, 1973). Byproduct S from sour-gas, fossil fuel combustion, and other sources now accounts for over 50% of S used by western countries, as shown in Fig. 9.1. This percentage may increase as pollution abatement measures increase the removal of SO2 from fossil fuel, particularly in the U.S.A. Atmospheric S, returned to the earth in rainwater, is also a very important source of S for plants. 

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