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Scheelite is a calcium tungstate mineral with the chemical formula Ca W O 4. It is an important ore of tungsten (wolfram). Scheelite is originally named after Swedish chemist Carl Wilhelm Scheele (1742–1786). Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws.
In chemistry, a tungstate is a compound that contains an oxyanion of tungsten or is a mixed oxide containing tungsten. The simplest tungstate ion is WO 2− 4 , "orthotungstate". [ 1 ] Many other tungstates belong to a large group of polyatomic ions that are termed polyoxometalates , ("POMs"), and specifically termed isopolyoxometalates as they ...
The plasma total calcium concentration is in the range of 2.2–2.6 mmol/L (9–10.5 mg/dL), and the normal ionized calcium is 1.3–1.5 mmol/L (4.5–5.6 mg/dL). [4] The amount of total calcium in the blood varies with the level of plasma albumin, the most abundant protein in plasma, and therefore the main carrier of protein-bound calcium in the blood.
The US Institute of Medicine (IOM) established Recommended Dietary Allowances (RDAs) for calcium in 1997 and updated those values in 2011. [6] See table. The European Food Safety Authority (EFSA) uses the term Population Reference Intake (PRIs) instead of RDAs and sets slightly different numbers: ages 4–10 800 mg, ages 11–17 1150 mg, ages 18–24 1000 mg, and >25 years 950 mg. [10]
Calcium is readily complexed by oxygen chelates such as EDTA and polyphosphates, which are useful in analytic chemistry and removing calcium ions from hard water. In the absence of steric hindrance, smaller group 2 cations tend to form stronger complexes, but when large polydentate macrocycles are involved the trend is reversed. [19]
Calcium is also required at other points in the coagulation cascade. Calcium ions play a major role in the regulation of coagulation cascade that is paramount in the maintenance of hemostasis. Other than platelet activation, calcium ions are responsible for complete activation of several coagulation factors, including coagulation Factor XIII. [43]
Though calcium is the most plentiful electrolyte in the body, a large percentage of it is used to form the bones. [14] It is mainly absorbed and excreted through the GI system. [14] The majority of calcium resides extracellularly, and it is crucial for the function of neurons, muscle cells, function of enzymes, and coagulation. [14]
4 or calcium tungstate: exhibits long decay time 9 μs and short wavelength emission with maximum at 420 nm matching sensitivity curve of bi‑alkali PMT. [7] The light yield and energy resolution of the scintillator (6.6% for 137 Cs) is comparable with that of CdWO 4. [53]