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ANALYTICAL METHODS/Mineral Analysis 107 Gumert WR (1998) A historical review of airborne gravity The Leading Edge 17: 113 117 http://www.aerogravity.com/carson2.htm Hansen R (1999) The gravity gradiometer: basic concepts and tradeoffs The Leading Edge 18: 478, 480 Hildebrand AR, Pilkington M, Connors M, Ortiz Aleman C, and Chavez RE (1995) Size and structure of the Chic xulub crater revealed by horizontal gravity gradients and cenotes Nature 376: 415 417 Hutton C (1778) An account of the calculations made from the survey and measures taken at Schiehallion, in order to ascertain the mean density of the Earth Phil Trans Royal Soc LXVIII: 689 788 McKenzie DP, Watts AB, Parsons B, and Roufosse M (1980) Planform of mantle convection beneath the Pacific Nature 288: 442 446 McKenzie DP and Nimmo F (1997) Elastic thickness esti mates for Venus from line of sight accelerations Icarus 130: 198 216 Milsom J (2002) Field Geophysics, 3rd edn Chichester, UK: John Wiley and Sons Sandwell DT and Smith WHF (1997) Marine gravity anom aly from Geosat and ERS satellite altimetry Journal of Geophysical Research 105: 10039 10054 (www.ngdc.noaa.gov) Smallwood JR, Staples RK, Richardson KR, White RS, and the FIRE working group (1999) Crust formed above the Iceland mantle plume: from continental rift to oceanic spreading center Journal of Geophysics Research 104(B10): 22885 22902 Smallwood JR, Towns MJ, and White RS (2001) The struc ture of the Faeroe Shetland Trough from integrated deep seismic and potential field modelling Journal of the Geo logical Society of London 158: 409 412 Smallwood JR and White RS (2002) Ridge plume inter action in the North Atlantic and its influence on contin ental breakup and seafloor spreading In: Jolley DW and Bell BR (eds.) The North Atlantic Igneous Province: Stratigraphy, Tectonic, Volcanic and Magmatic Pro cesses, pp 15 37 London: Geological Society of London, Spec Publ 197 Smith WH and Sandwell DT (1997) Global Sea Floor Top ography from Satellite Altimetry and Ship Depth Sound ings Science 277: 1956 1962 Telford WM, Geldart LP, and Sheriff RE (1990) Applied Geophysics, 2nd edn Cambridge, UK: Cambridge Uni versity Press Watts AB (2001) Isostasy and Flexure of the Lithosphere Cambridge, UK: Cambridge University Press Mineral Analysis N G Ware, Australian National University, Canberra, ACT, Australia ß 2005, Elsevier Ltd All Rights Reserved Mineral Analysis Mineral analysis involves determining the chemical relationships between and within mineral grains Microanalytical techniques are essential, and methods include X-ray spectrometry and mass spectrometry Electron probe and laser ablation procedures are commonly used techniques for major and trace element analysis, respectively (see Analytical Methods: Geochemical Analysis (Including X-Ray)) A chemical analysis of a mineral is expressed as a table of weight percent (wt.%) of its component elements or oxides Concentrations lower than about 0.5 wt.% are often expressed as parts per million (ppm) by weight of element These mineral analyses are easily converted into atomic formulas and thence into percentages of the end-member ‘molecules’ within the mineral group (see Table 1) Mineral analyses are used in descriptive petrology, geothermometry, and geobarometry, and in the understanding of petrogenesis Sometimes thousands of analyses are collected in the completion of a single research project Large amounts of data are presented graphically, plotting concentrations of elements or ratios of elements against each other, thus illustrating chemical trends or chemical equilibrium (see Figure 1) In addition to the chemical analysis, a complete description of a mineral requires a knowledge of its crystallography Both chemical composition and crystallography are required to predict the behaviour of minerals, and hence rocks, in geological processes The discovery of each new mineral involves the determination of its crystal structure as a matter of routine using X-ray and electron diffraction techniques Thus, when a monomorphic mineral is identified from its composition, its crystallography follows Polymorphs may be identified by optical microscopy Whereas it is sometimes convenient to identify an unknown mineral from its diffraction pattern, and although cell parameters can be used as a rough measure of end-member composition, crystallography no longer plays a major role in quantitative mineral analysis It was once necessary to separate a mineral from its parent rock by crushing, followed by use of heavy liquids and magnetic/isodynamic separators Up to a
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