Summary: A Tertiary dolerite plug at Carneal, Co. Antrim has been contaminated by Chalk with the production of calc-silicates and related minerals. In a larnitespinel-rock the spinel is of the unusual ferrian variety. It has the composition (Mg6·82Fe0.76″Mn0·12Ni0·01Zn0·01)(Al11·2Fe4.94‴Ti0·03)O32. The spinel, which is brown, has: n, 1·862; D, 3·97; a, 8·1905 Å. A chemical analysis and powder data are given, the implications of experimental data are briefly discussed, and the nomenclature is reviewed.