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    Adsorption study of sesbania gum onto calcite surface: Implications for smithsonite-calcite flotation separation
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    Fungi may play a far more important role in carbonate diagenesis than has been previously suspected. This can be demonstrated by placing known species of fungi on crystals of Iceland spar calcite. Such experiments show that fungi can (1) cause sparmicritization through dissolution, (2) produce spiky calcite through dissolution, (3) trap and bind loose particles of calcite, and (4) promote the growth of new calcite crystals. Although not observed in this series of experiments, fungi can bore into substrates and cause sparmicritization. The activity of fungi involves a complex interplay of substrate destruction and construction without the intervention of vast quantities of fluid.
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    The compressibility of calcite to 40 kbar has been remeasured by using a piston-cylinder apparatus. Calcite 1 is found to transform to calcite 2 at 14.5 kbar with a volume change of 0.00483 cm3/g, and calcite 2 is found to change to calcite 3 at 17.4 kbar with a volume change of 0.01291 cm3/g. The volume compression data for the three phases are described by the following quadratic relations: Calcite 1 Calcite 2 Calcite 3 where P is pressure in kilobars. The compression data for calcite 1 and calcite 3 are in good agreement with those available in the literature. The data exhibiting an abnormally high compression of calcite 2 have been reported for the first time. The compression data for calcite 2 have been used to explain quantitatively the abnormal drop near 15 kbar observed in the ultrasonic sound velocity in calcite.
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    ABSTRACT Mineralogical analysis of calcite and Mg‐calcite by X‐ray diffraction requires that the samples be ground to a powder. Such grinding determines the particle size of the powder and the structural damage of the minerals. Both of these in turn affect the peak intensities recorded by the X‐ray machine. Most carbonate sediments are inhomogeneous; they contain both calcite and Mg‐calcite which are affected differently by grinding. Such differences cause quantitative analytical results to be inconsistent with the true mineralogical abundance. The two acceptable methods of analysis—(1) measurement of peak height from the base and (2) measurement of the area under the peak—were compared to determine if sample preparation affects the quantitative results. In samples with variable and relatively small amounts of calcite and Mg‐calcite the measurement of peak height yields more reproducible results than does the measurement of peak areas. Different proportions of particle size of the mineralogical components in a sample powder, affect proportionally more the peak areas than the peak heights. Extensive grinding causes structural damage of the component minerals which affects much more the peak areas than the peak heights. Thus for quantitative analyses of calcite and Mg‐calcite in inhomogeneous carbonate samples which require differing grinding times and have greatly variable amounts of calcite and Mg‐calcite, the peak height measurement seems to be a better method than peak area measurement.