Silicate rocks

The element is found in niobite (or columbite), niobite-tantalite, parochlore, and euxenite. Large deposits of niobium have been found associated with carbonatites (carbon-silicate rocks), as a constituent of parochlore. Extensive ore reserves are found in Canada, Brazil, Nigeria, Zaire, and in Russia. 

A. Soutar, S. R. Johnson, and T. R. Baumgartner, in C. Isaacs and J. Garison, eds.. The Monterey Formation and Related Siliceous Rocks of California, Society of Economic Paleontologists and Mineralogists, 1981, p. 123. 

Vitreous, colourless form of free silica. Formed when quartz is heated to 870°C (1598°F). Aporous siliceous rock resulting from the decomposition of chertorsiliceous limestone. Used as a base in soap and scouring powders, in metal polishing, as a filtering agent, and in wood and paint fillers. A cryptocrystalline form of free silica. 

Oxygen is the most abundant element on earth. The earth s crust is rich in carbonate and silicate rocks, the oceans are almost entirely water, and oxygen constitutes almost one fifth of the air we breathe. Carbon ranks only fourteenth among the elements in natural abundance, but trails only hydrogen and oxygen in its abundance in the human body. It is the chemical properties of carbon that make it uniquely suitable as the raw material forthe building blocks of life. Let s find out more about those chemical properties. 

Graphite is widely distributed throughout the world though much of it is of little economic importance. Large crystals or flake occur in metamorphosed sedimentary silicate rocks such as quartz, mica schists and gneisses crystal size varies from <1 mm up to about 6 mm (average 4mm) and the deposits form lenses up to 30 m thick stretching several... 

C O Ingamells Rapid chemical analysis of silicate rocks. Talanta, 1964, 11, 665... 

P J Potts A Handbook of Silicate Rock Analysis, 2nd edn. Blackie and Son Ltd, Glasgow, 1987... 

Dunne, T. (1978). Rates of chemical denudation of silicate rocks in tropical catchments. Nature 274, 244-246. 

The Lux-Flood theory relates to oxide melts. Geologists have often used acid-base concepts for the empirical classification of igneous silicate rocks (Read, 1948). Silica is implicitly assumed to be responsible for acidity, and the silica content of a rock is used as a measure of its acid-base balance ... 

Abbey S (1980) Studies in Standard Samples for use in the general analysis of Silicate Rocks and Minerals, Part 6 1979 Edition of Usable Values. Pap - Geol Surv Can Paper 80-14. 

Fairbairn HW et al. (1951) U.S. Geological Survey Bulletin 980. A cooperative investigation of precision and accuracy in chemical, spectrochemical and modal analysis of silicate rocks. 71 pp. 

Stevens RE et al. (i960) Second report on a cooperative investigation of the composition of two silicate rocks. U.S. Government Printing Office, Washington DC, 126 pp. 

An alternative to the bridge technique was recently reported for thorium analysis in silicate rocks for which both Th and Th are measured on a single lon-counting detector (Rubin 2001). With careful chemistry and mass spectrometry, °Th/ Th ratios of igneous rocks can be measured with this technique with a precision that is similar to the bridge method. The disadvantage of this technique is that °Th ion-count rates are extremely low (around 10 cps) with normal silicate thorium ratios and are therefore subject to perturbations from background variation and low-level isobaric interferences in normal samples. 

Analysis is possible on high-" " Th silicate rocks, as well as low- Th carbonate samples... 

Thorium. Multiple-collector measurement protocols by TIMS for thorium isotopic analysis typically involve the simultaneous measurement of Th and °Th (for silicate rocks), or Th and °Th, then Th and Th (for low- Th samples), using an axial ion counter and off-axis Faraday collector (Table 1). Various methods are used to correct for the relative gain between the low-level and Faraday detectors and 2a-uncertainties of l-5%o are typically obtained (Palacz et al. 1992 Cohen et al. 1992 McDermott et al. 1993 Rubin 2001). Charge-collection TIMS protocols enable Th, °Th and Th to be monitored simultaneously on a multiple-Faraday array and can achieve measurement uncertainties at the sub-permil level (Esat et al. 1995 Stirling et al. 1995). 

Bourdon B, Joron J-L, Allegre CJ (1999) A method for Pa analysis by thermal ionization mass spectrometry in silicate rocks. Chem Geol 157 147-151... 

Nakai S, Fidcuda S, Nakada S (2001) Thorium isotopic measurements on silicate rock samples with a multicollector inductively coupled plasma mass spectrometer. Analyst 126 1707-1710... 

Around 85% of the total amount of hydrogen is present as a metallic phase. It is assumed that there is a silicate rock core with a temperature estimated to be... 

Caldeira, K., Forests, climate, and silicate rock weathering, /. Geochem. Exploration, 88(1-3), 419 (Special Issue), 2006. 

Siroc [Silicate rock] Also known as the one-shot system. A chemical grouting system for hardening ground formations. Aqueous solutions of sodium silicate and formamide are mixed and injected into the ground the formamide slowly reacts with the silicate, precipitating hydrated silica, which binds the soil particles together. Invented in 1961 by the Diamond Alkali Company. See also Joosten. 

Nuclear bombardment reactions in which the product is radioactive constitute the basis of radioactivation analysis (p. 456). Although in principle any bombardment-decay sequence may be used the analyst is largely concerned with thermal neutron activation. Equation (10.13) relates the induced activity to the amount of the parent nucleide (analyte). However, practical difficulties arise because of flux inhomogeneities. It is common therefore to irradiate a standard with very similar characteristics alongside the sample, e.g. for a silicate rock sample a standard solution would be evaporated on to a similar amount of pure silica. On the assumption that identical specific activities for the analyte are then induced in the sample and standard, the amount w2 of analyte is readily calculated from... 

Table 8.9 shows an analysis of a silicate rock and compares the precision of X-ray fluorescence analysis with wet chemical methods and arc/spark emission spectrometry. 

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