The chemistry and mineralogy of some granulated and pelletized blastfurnace slags

Samples of granulated slag from Scunthorpe, Humberside, collected over several years, vary somewhat in chemical composition reflecting differences in iron-making 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-SiO2-Al2O3-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 Al (< 11 % Al2O3) British and French slags are approaching an optimum composition.

Origin of appinitic pockets in the diorites of Jersey, Channel Islands

SummaryIsolated pockets of pegmatitic appinite characterized by hollow-shell, prismatic amphiboles are common in the Pre-Cambrian metagabbros and metasomatic diorites of Jersey. Field relationships and petrography indicate a liquid phase in the formation of these appinitic pockets, which are chemically distinct from the associated gabbros and diorites. Close chemical ties between appinites and host rocks, however, prove a replacive, metasomatic, rather than intrusive origin for the pockets. Significant enrichment in SiO2, K2O, and Na2O suggest that surrounding granite provided the metasomatic agents. The localized changes in composition of the basic rocks resulted in the formation of partially molten pockets from which the appinites crystallized. This mechanism probably necessitates a temperature in the region of 900 °C at 2–5 Kb PH2O: Fractured, hollow-shell, prismatic amphiboles of the pockets are consistent with quench crystallization, possibly due to the sudden loss of volatiles. An increase in the oxygen fugacity may have played a major role in inducing the rapid crystallization of kaersutitic amphibole. The envisaged conditions under which these changes took place are those of a high-level, sub-volcanic environment.