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Different techniques are used in the analysis of a suite of subcontinental, mantle-derived kaersutite (hornblende) minerals to determine their crystal and chemical composition. The ferrous valence and site occupancies are determined by Mossbauer spectroscopy and the bulk hydrogen contents are obtained by uranium extraction methods. The fluorine content is measured by proton-stimulated gamma-ray emission and chemical composition of the methods. Ferrous and hydrogen are present in equal proportions, revealing that these minerals lost a part of their hydrogen during the process of entrainment and ascent.

The precise analysis of oxygen is now possible with the introduction of new and sophisticated electron microprobe instruments. However, electron microprobes do not accurately calibrate oxygen because of the lack of standard oxygen measurements. Furthermore, the lack of standards leads to less rigorous evaluation of the results of oxygen analyses. The development of standards in the measurement of oxygen is expected to lead to the calibration of electron microprobes for more accurate analyses of oxygen.

A study on the defect microstructure and oxidation state of iron in two olivine crystals from the Dish Hill cinder cone in California's Deadman Lake Volcanic Field was presented. The crystals were subjected to polarized infrared spectroscopy, transmission electron microscopy and Mossbauer spectroscopy to determine their composition. Results indicate that the crystals contained individual layers of laihunite.

Petrologists are generally faced with the dilemma of estimating [Fe.sup.2+/Fe.sup.3+] ratios for minerals on the basis of microprobe analyses that only identify total iron, commonly given as FeO. Common solutions to this problem include the assumption that all iron is ferrous, or simply calculating [Fe.sup.3+] on the basis of stoichiometry from the microprobe analyses. In order to test these assumptions, ferric iron content has been directly measured on Al-augite, kaersutite, and spinel high-pressure megacrysts from alkali basalts by using the technique of Mossbauer spectroscopy. Measured [Fe.sup.3+] content does not agree with [Fe.sup.3+] calculated from microprobe analyses. Calculated [Fe.sup.3+] content varies widely between three augite megacrysts that have nearly identical microprobe analyses and consistent Mossbauer [Fe.sup.3+] values. Ferric iron calculations are found to be highly sensitive to very slight variations in Si, 1+, 3+, and 4+ cations, and should be considered generally unreliable. Mantle petrologists generally assume low or neglible ferric iron content in mantle minerals. This study found that 28%-40% of iron was ferric in these eight megacrysts. Similarity of Al-augite and kaersutite megacryst compositions to minerals in mantle xenoliths suggests that minerals in mantle xenoliths may have higher [Fe.sup.3+] content than generally believed.