Limestone weathering

Macpherson, G.L. Roberts, J.A. et al. 2008. Increasing shallow groundwater C02 and limestone weathering, Konza Prairie, USA. Geochimica et Cosmochimica Acta, 72, 5581-5599. 

Fig. 5.6 Relationship between pH, alkalinity and dissolved calcium ions in stream waters in the Malham Tarn area of northern England, flowing from bog on siliceous mudrock to limestone. Note that pH is buffered around 8 once limestone weathering begins. Data from Woof and Jackson (1988).

Limestone Weathering in an Urban Environment Illustration of the Interaction of the Three Factors... 

Dense limestones weather well and easily meet the requirement in the Highways Agency s Specification [8.7] of a magnesium sulfate soundness value [8.4] greater than 75 %. 

Trudgill, S.T. and Viles, H.A. 1998. Field and laboratory approaches to limestone weathering. Quarterly... 

Ratios of U and U to Th and Ra daughters, combined with differences in chemical reactivity have been used to investigate the formation and weathering of limestone in karst soils of the Jura Mountains, and of the mountains in the central part of Switzerland. Uranium contained within calcite is released during weathering, and migrates as stable uranyl(VI) carbonato complexes through the soil. In contrast, the uranium decay products, Th and Ra,... 

Barite [13462-86-7], natural barium sulfate, BaSO, commonly known as barytes, and sometimes as heavy spar, tiU, or cawk, occurs in many geological environments in sedimentary, igneous, and metamorphic rocks. Commercial deposits are of three types vein and cavity filling deposits residual deposits and bedded deposits. Most commercial sources are replacement deposits in limestone, dolomitic sandstone, and shales, or residual deposits caused by differential weathering that result in lumps of barite enclosed in clay. Barite is widely distributed and has minable deposits in many countries. 

More CO2 can actually be absorbed chemically into the ocean than the above reaction sequence suggests. Terrestrial weathering of rocks containing carbonate, such as limestone, and subsequent aerial or riverine transport, means that the ocean is enriched in carbonate. Keeping and Kj constant implies, through eqns. (3) and (4), that enhancing the oceanic [COj ] leads to a greater level of... 

U/ 32jj activity ratio of -0.8 (equivalent to a Th/U weight ratio of 3.8), and this is often taken to represent that of the host rocks in the absence of direct measurements, although this can of course be substantially different in rocks such as limestones or other sedimentary deposits. If it is assumed that the groundwater profile is in steady state, that weathering and precipitation are not important for these nuclides, and that the parent nuclides ojh and have similar behaviors, then the corresponding terms in... 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

FIGURE 44 Weathering. A weathered sandstone column. Calcite (composed of calcium carbonate) is dissolved by rain and groundwater (see Textbox 73). When stone in which calcite is a main component as, for example, sandstone, limestone, and marble, is in contact with water for long periods of time, it is weathered and partly or entirely dissolved. Pollutants such as sulfur dioxide are fundamental in accelerating the weathering and dissolution process. When sulfur dioxide, for example, dissolves in rainwater, it forms sulfuric acid, a strong acid that, at ambient temperatures, rapidly dissolves calcium carbonate. 

Vinegar is recommended for cleaning a variety of appliances and other items that may be stained by hard water deposits. Automatic coffee makers, steam irons, dishwashers, teapots, faucet heads, and shower heads — over time, all accumulate calcium deposits from hard water. Groundwater, that is, water that travels through soil and rocks, accumulates dissolved calcium ions as a consequence of the natural weathering of minerals that contain calcium such as limestone and calcite, shells, and coral. At the same time, carbon dioxide in the air dissolves in water to form carbonate ions that combine with calcium ions to form a white solid, calcium... 

The action of carbonic acid on limestone produces a calcium bicarbonate solution that is exceedingly soluble in water. (For comparison, at 20°C the solubility of calcium carbonate in water is only 0.0145 g per liter while the solubility of calcium bicarbonate is 166 g per literJ ) Magnesium ions from dolomite are also released into aqueous solution according to the same mechanism. The weathering of gypsum, calcium sulfate, also releases calcium ions into natural water supplies. 

Wood, H. K. Macpherson, G.L. 2005. Sources of Sr and implications for weathering of limestone under tallgrass prairie, northeastern Kansas. Applied Geochemistry, 12, 2325-2342 doi 10.1016/ j.apgeochem.2005.08.002. 

Edmond JM (1992) Himalayan tectonics, weathering processes, and the strontium isotope record in marine limestones. Science 258 1594-1597... 

This is a very sketchy depiction of the deep carbon cycle because it illustrates only the behaviors of calcium and silica. In reality, a wide variety of other cations are present in the silicate minerals, such as in the plagioclase feldspars (Table 13.2). Furthermore, not all of the limestone is converted into siUcate minerals some remains as limestone. Uplift of the limestone onto land, followed by chemical and biological weathering, is another sink for atmospheric CO2, via... 

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