76 ANALYTICAL METHODS/Geochemical Analysis (Including X-ray) collecting the fluid for conventional water analysis (inductively coupled plasma techniques, ion chromatography) Fluid inclusions are listed here since they are most commonly analysed by using a high powered microscope and heating–cooling stage Most fluid inclusions are composed of discrete liquid and vapour phases even though they would have been trapped as a single-phase liquid, which is typically assumed to have been saturated with vapour at the time of trapping During a heating cycle, the two phases homogenize; the precise temperature of homogenization reveals the temperature at which the mineral grew The salinity of the water can be assessed by monitoring the temperature at which it starts freezing, since this temperature can be related to salt content (assuming that the water is dominated by dissolved NaCl) A combination of thorough petrography and thermometric studies of aqueous inclusions can help to reveal details of the thermal and mineral-growth history as well as the fluid evolution history Related Geochemical Techniques The techniques listed and briefly discussed here are only some of the vast panoply of techniques that have been employed during geochemical studies over the last 50 years or so Some have now fallen out of favour For example, a technique called neutron activation analysis was used for a long time to measure trace elements in solids It has fallen out of favour mainly owing to developments in ICP-OES and ICP-MS The vast range of light and electron optical techniques are routinely used in conjunction with a wide range of solid-state and even organic geochemical studies Scanning electron microscopy has recently been extensively developed and can now give fabric, mineralogy, mineral chemistry, and high-resolution crystallographic information Transmission electron microscopy can provide ultra-high spatial resolution (of the order of tens of nm) geochemical data (using secondary X-rays) as well as fabric and crystallographic data A wide range of wet geochemical techniques have been employed routinely in studies of natural waters from all near-surface and surface environments Titration, electrochemical techniques, and colorimetry are essential techniques that are used routinely in many geochemical studies See Also Clay Minerals Fluid Inclusions Minerals: Definition and Classification; Native Elements Petroleum Geology: Chemical and Physical Properties; The Petroleum System Rocks and Their Classification Further Reading Emery D and Robinson AC (1993) Inorganic Geochemistry: Applications to Petroleum Geology Oxford: Blackwells Farmer VC (1974) The Infrared Spectra of Minerals London: Mineralogical Society Faure G (1986) Principle of Isotope Geology New York: John Wiley and Sons Goldstein RH and Reynolds TJ (1994) Systems of Fluid Inclusions Tulsa: Society of Sedimentary Geology Hagemann HW and Hollerbach A (1986) The fluorescence behaviour of crude oils with respect to their thermal maturation and degradation Organic Geochemistry 10: 473 480 Jarvis I and Jarvis KE (1992) Plasma spectrometry in the Earth sciences: techniques, applications and future trends Chemical Geology 95: 33 Jenkins R (1999) X ray Fluorescence Spectrometry New York: Wiley Interscience Lico MS, Kharaka YK, Carothers WM, and Wright VA (1982) Methods for the Collection and Analysis of Geo pressured Geothermal and Oil Field Waters Water Supply Paper 2194 United States Geological Survey Moore DM and Reynolds RC (1997) X ray Diffraction and the Identification and Analysis of Clay Minerals Oxford: Oxford University Press Rollinson HR (1993) Using Geochemical Data: Evalu ation, Presentation, Interpretation New York: Longman Scientific and Technical Tissot B and Welte D (1984) Petroleum Formation and Occurrence Berlin: Springer Verlag Tucker ME (1988) Techniques in Sedimentology Oxford: Blackwell Scientific Weiss J (2000) Ion Chromatography New York: John Wiley and Sons Zussman J (1967) Physical Methods in Determinative Mineralogy London: Academic Press