Chuara is a sill which forms a hill some 300 m high and 3 km in length. The sill is probably 150-190 m in maximum thickness and rests on Karoo shales which are metamorphosed, as are dolerites cutting the shales. North of the hill are granite gneisses within which are dykes of solvsbergite and phonolite. The sill is of aegirine foyaite which consists of orthoclase, nepheline, prisms of aegirine, tiny magnetites and in places drusy areas of analcime with central carbonate. The phonolite of the dykes consists of minute nepheline, aegirine and orthoclase laths.