Grains calcium source

Presolar grains Excess 41K exists in Ca-rich presolar grains, in proportion to the amount of calcium. This identifies extinct 41Ca is the source of these 41K excesses. That41 Ca was alive when the stellar grains condensed rather than in the early solar system. See 41Ca for more on that extinct radioactivity (see Glossary). 

The main sources of dietary calcium are milk and dairy products. In the United States, it is estimated that 73% of calcium is obtained from milk products, 9% from fruit and vegetables, 5% from grains, and about 12% from all other sources combined. The optimal intake of dietary calcium depends on age, gender, and physiological status and is summarized in Table 30-2. 

Presolar grains exhibit large isotopic anomalies not only in their major elements, but also in many minor elements. Isotopic ratios vary over many orders of magnitude, indicative of contributions from different types of stellar sources, namely evolved stars, novae, and SN explosions. Isotope anomalies are also seen in objects with Solar System origin, which, however, are much smaller than those in presolar grains. For example, the calcium-aluminum-rich inclusions (CAIs), the earliest... 

Inadequate amounts of dietary calcium contribute to loss of bone mineral density and increased rates of fracture observed in osteoporosis, a disease which afflicts over 40% of postmenopausal women in the developed nations. The primary source of dietary calcium is dairy products (Table 3). The preparation of com meal using calcium hydroxide fortifies this grain. Because the intake of dairy products by adult females is low, their average calcium consumption (550 mg) is well below the recommended 1000 1200 mg. Supplementation with various forms of calcium is pmdent. Fortification of fhiit juices and soft drinks with calcium complexed with citric and malic acids has been achieved. 

Northwest Africa Oil (NWA 011) has briefly been described by Afanasiev et al. (2000) and more extensively by Yamaguchi et al. (2002), the source of most information presented here. NWA Oil is composed of relatively coarse, anhedral pigeonite and augite, and fine-grained, mostly interstitial plagioclase with a recrystallized texture, interpreted to indicate that it is a recrystallized breccia. Minor phases are silica, chromite, ilmenite, calcium phosphate, ferroan olivine, troilite, and baddeleyite. Pyroxenes make up... 

Detrital feldspars in modern sediments have a compositional range that reflects their composition in the source rocks (Trevena and Nash, 1981). During diagenesis, sodium-rich K-feldspars and more calcium-rich detrital plagioclase grains are more subject to dissolution (and replacement) than potassium-rich K-feldspar or sodium-rich plagioclases (Maynard, 1984 Milliken, 1988, 1992 Milliken et al, 1989). 

Dietary sources of calcium are dairy products, eggs, green leafy vegetables, broccoli, legumes, nuts, and whole grains. (Less than 30% of calcium in food is absorbed.) Calcium is absorbed in the small intestine. The amount of absorption depends on the serum calcium level and availability of vitamin D. There is reduced absorption of calcium if there is a high serum calcium level or a low vitamin D level. 

Where a skeletal source cannot be identified, calcium carbonate (CaC03) grains and finegrained muds may be of abiological origin. The most famous occurrences occur in shallow, warm, saline waters of the Bahamas and the Arabian Gulf. In these areas two distinctive morphologies are present, ooids and needle muds (Fig. 1). 

Major dietary sources of calcium are milk and dairy products, such as cheese and yogurt. Cow s milk contains 120 mg of Ca + per deciliter (30 mmol/L) and is now usually supplemented with vitamin D. Sardines (and other small fish whose bones are consumed) and soybean products can provide significant amounts of calcium. Soybean curd, known as tofu and eaten widely in China and Japan, contains 128 mg of Ca " " per 100 g. Dark green leafy vegetables, legumes, nuts, and whole-grain cereal products contribute to dietary calcium. 

Shell-rich layers in the Pliocene sandstones are not preferentially cemented. This suggests that the source of calcium ions was so uniformly distributed that there was no tendency to preferentially cement the shell layers. This contrasts with cemented shell-rich layers noted by other workers (e.g. Davies 1969 Fiirsich, 1982 Kantorowicz et al., 1987). Large amounts of carbonate grains remain in the host sandstones we studied cementation did not cease because of a lack of available calcium. 

The calcium in calcite cement was also derived chiefly from the large reservoir of calcium in CRFs and skeletal grains in the sandstones and, where present, interbedded mudrocks. Some calcium in cement in the deepest buried formations may be derived from albitized plagioclase, but this source was probably minor compared with CRFs and carbonate skeletal grains. 

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