Calcareous rocks

Dissolution of CaCOs is a congruent reaction the entire mineral is weathered and results completely in soluble products. The above reaction is driven to the right by an increase of CO2 partial pressure and by the removal of the Ca and/or bicarbonate. Any impurities present in the calcareous rock, such as silicates, oxides, organic compounds, and others, are left as residue. As the calcium and bicarbonate leach... 

Uranium series Relative amounts of parent-and daughter-isotope Calcareous rocks, shell Textbox 16... 

The Ebro headwaters flow on calcareous substratum, specifically sandstone and calcium marls, from the Triassic, Cretacic, and Jurassic. During the Quaternary, at the plain of La Virga (Reinosa), a shallow lake accumulated the deposits of siliceous sandrocks. This old highland lake is now the Embalse del Ebro reservoir. From that point downstream to Conchas de Haro the main channel flows on calcareous rocks from the Cretacic, highly resistant to the erosion. 

Table 11.5 shows that sedimentation rates of 0.1 - 2 g nr2 d 1 are typically observed in lakes still higher values are found in very eutrophic lakes. The settling material can be collected in sediment traps it can then be characterized in terms of chemical composition, morphology, and size distribution of the particles. The composition is subject to seasonal variations caused primarily by different biological activities in the various seasons. Representative examples for Lakes Zurich and Constance are given in Fig. 11.10. These two lakes are prealpine lakes, located in regions of predominantly calcareous rocks, both are under the influence of eutrophication. 

Sulphate of magnesia is also obtained by the action of sulphuric acid upon calcareous rocks rich in carbonate of magnesia, such as dolomite. The compound is calcined, and reduced to powder by being aspersed with water it is then diffused through water, and sulphuric acid is added sulphate of lime and sulphate of magnesia are formed, the one barely soluble in water, and the other very much so consequently, they are readily separated. 

Approved lists are also open to interpretation. An example is calcium carbonate, an approved organic source of Ca. Is ground limestone, a natural and common source of calcium carbonate and prepared from mined calcareous rock, approved as calcium carbonate It is a well-established ingredient in conventional poultry diets and one assumes that it is acceptable in organic diets. In cases such as this the producer should verify with the certifying agency that this interpretation is correct. This example adds weight to the conclusion of Wilson (2003) in Chapter 1 (this volume) that it would be very helpful if lists of approved feedstuffs could be very specific. 

Wollenzien, U., de Hoog, G. S., Krumbein, W. E. Urzi, C. (1995). On the isolation of microcolonial fungi occurring on and in marble and other calcareous rocks. Science of the Total Environment, 167, 287-94. 

For example, lakes in drainage basins of easily weathered soils such as calcareous rocks (calcite, dolomite, gypsum, halite) generally have high values of pH, alkalinity, total dissolved solids, conductivity, and hardness. Such is the case for lakes located in cavities formed through the gradual dissolution of water-soluble rocks (solution or Karst lakes). On the other hand if the drainage basin is in an acidic rock basin (i.e., where silicates predominate and are difficult to weather), the water has an acidic pH, low alkalinity, and low total dissolved solids. 

The CO2 content in warmer zones is higher due to an increase in the metabolic rates and CO2 production, which in turn favors an increase in water hardness in surface and groundwaters surrounded by calcareous rocks. For example, average values of pH, HCO3 and hardness of groundwater in the state of Texas (USA) are 6.9, 316 ppm, and 264 ppm of CaCC>3, respectively, whereas these values... 

Though water acidification is one of the most important aspects, one would certainly not expect significant changes in water acidity in all exposed areas. The effect is highly dependent on bedrock geology and the nature of the overburden. No acidification of fresh water is to be expected in areas with appreciable amounts of calcareous rocks. The most well known susceptible areas are those with shallow overburden and quartzbearing bedrock. Acidification can occur in catchments with highly weathered sandy soils with low neutralization capacities. 

Phosphorite, for our purposes, is the term applied to calcium phosphate rocks, whether they are accumulations of bones, precipitates directly from sea water or replacements of calcareous rocks. They are very extensive on the earth, occurring on all continental land masses with the possible exception of Antarctica, where commercial deposits have not yet been found. Phosphorites comprise the principal geologic storage bin for inorganic phosphates. 

General Burgoyne mentions seeing the same device in use in blasting the calcareous rocks of Marseilles, at the foot of the hill on which the fort of Notre Dame de la Garde now stands. 

Beds of epi-minerals, i.e. impregnated non-calcareous rocks. In this case the anthuoiiy ore is impregnated in the rocks. Hereaftei this is denoted by C. 

The trend of major elements in water and soil is illustrated in Fig. 12C. As expected, the spring waters are the most Ca-enriched waters of all the yet presented examples. Moreover, the two upper horizons (A and B), rich in Si, are very different from the Ca-rich C-horizon. Most of the elements present in soil solution (Fig. 12D, Appendix A.5) were dissolved in the upper soil horizon but, due to an increase of pH, their concentrations in solution decrease strongly as soon as the water gets in contact with the underlying calcareous rock. That explains the low trace element concentrations, measured in the springs. These decreases in concentration can be attributed to the precipitation of Al, Fe and Mn as oxy-hydroxide with which trace elements are coprecipitated or adsorbed. Some elements, such as Cd, Pb and Ni can also precipitate as carbonate or be adsorbed on calcite. 

For location at or near a mine site, the disposal of sulphur dioxide is rather a different proposition than for smelters located remotely fixrm the mine. Marketing of sulphuric acid is unlikely from most mine sites but safe disposal by reaction of SO2 with calcareous rocks to form insoluble sulfates is an option since often the host rock to polymetallic sulphides is carbonaceous. There is no single answer to this question except that, whatever the location, the sulphur must be safely captured and disposed of and that this does not demand any novel technology but will incur some cost penalty. 

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