Thirty analyses of each of nine well-characterized silicate glasses and minerals have been made, using a Link Systems Model 290-2KX energy-dispersive spectrometer, fitted to a Cambridge Geoscan. Statistical analysis of the analytical data shows that the accuracy and precision of energy-dispersive analyses are comparable to wavelengthdispersive analyses, provided that more than about 1 wt % of each element of interest is present. The detection limits for different elementsvary according to the nature of the sample, the element concerned and the counting time. For 100 liveseconds counting times the detection limits are in the range from 0.05-0.26 wt % of element. program for processing electron microprobe analytical data. EMPADR VII.

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A B S T R A C T. Samples of granulated slag from Scunthorpe, Humberside, collected over several years, vary somewhat in chemical composition reflecting differences in ironmaking practice. All contain some melilite and oldhamite crystals and minor amounts of iron along with the glass. Granulated slag from Usinor, Dunkirk, France, has a little more CaO than the Scunthorpe material with crystals of merwinite and oldhamite. Pelletised slag from Redcar, Teeside, is much more vescicular than the granulated material and contains melilite and oldhamite.The melilite crystals contain many inclusions of oldhamite and iron. They span a wide range within the akermanite-gehlenite series and are non-stoichiometric in composition. The merwinite may have formed largely by quench crystallization. Oldhamite is probably the first phase to form in all the slags. The silicate mineralogy can be explained in terms of the phase relationships within the CaO SiO 2 A12Oa-MgO quaternary system. The small difference in composition of the French slags is sufficient for them to fall into the primary phase field of merwinite rather than melilite. Assuming that only a minor proportion of crystals is acceptable in slags for use in Portland Blastfurnace Cement, the present low A1 (< 11 ~ A1203) British and French slags are approaching an optimum composition.

Direct analysis of the separated phases in unmixed sodium borosilicate glasses has been carried out using an electron microprobe analyzer. The results are discussed in relation to the tie-lines proposed by Charles,' Tran,Z and Ma~urin.~

A microscopic and electron microprobe investigation has been made of six samples of the allivalite-chromitite-peridotite band at the junction of Units 11 and 12, Eastern Layered Series, Rhum. Analyses are presented of olivine, plagioclase and pyroxene, the plagioclase showing reverse zoning in the chromitite. Sulphide droplets occur within and above the chromitite, and contain pyrrhotite, pentlandite, cubanite, bornite, digenite, chalcocite, native copper and electrum, as well as chromite zoned to magnetite, spinel and ilmenite. The variation from aluminous chromite to chromite in the chromitite is confirmed by analyses of five new traverses. The rocks formed during and just after the time when new magma entered the magma chamber. The variation in the chromite compositions is ascribed mainly to magmatic variation in composition due to the mixing process.