Al-rich pyroxene and melilite in a blast furnace slag and a comparison with the Allende meteorite

CaA12SiO6) and melilite containing 69-43 ~ gehlenite crystallized from a blast-furnace slag at atmospheric pressure between about I45O ~ and 125o ~ The occurrence is of petrological interest because the association of pyroxene with gehlenite-rich melilite has not been recorded from experimental studies in the system CaO-MgO-A1203-SiO2, and because of the similarity of the compositions ofboth minerals to pyroxene and melilite in the Ca-Al-rich inclusions of the Allende meteorite. S L A G composition. The slag was produced at the Corby works of the British Steel Corporat ion in February I973, and is within the normal range of composit ions of blast-furnace slags being produced at Corby at that time. The slag was cast into an approximately hemispherical ladle 2 m in diameter and allowed to cool for a day before being t ipped out. The nearly solidified 'ball ' broke, leaving a central cavity from which some sti l l-molten slag may have run out. Samples were obtained from the chilled margin at the outermost i0 cm of the ball and from the coarse-grained interior at a point about 60 cm from the outside. Chemical analyses of the slag at 2- 4 cm and at 60 cm from the outside are given in Table I. Estimates of cooling rates based on heat conduct ion show that the sample at 2- 4 cm crystall ized in a matter of minutes