Tricalcium disilicate (rankinite), a new mineral from Scawt Hill, Co. Antrim (With Plate V)

Tricalcium disilicate, first described by Shepherd, Rankin, and Wright in their investigations on the lime–silica and lime–alumina–silica systems has since been reported as a constituent of technical slags. An account has also been given of its occurrence as a reaction product in a glass furnace. In the ternary system CaO–Al2O3–SiO2 the compound forms with pseudowollastonite–gehlenite and larnite–gehlenite two three-phase equilibrium assemblages, associations which are in part recorded in the technical products. G. V. Wilson recorded the disilicate together with wollastonite and melilite in reconstituted limestone fragments enclosed in glass, while S. G. Gordon has described and presented an analysis of a slag composed of pseudowollastonite and the 3:2-compound approaching in composition that of the binary eutectic in the synthetic system.