Adjacent to the border with Niger in northern Nigeria over a level plain of blown sand rise occasional rocky hills of arfvedsonite granite with a few volcanic rocks. The area underlain by these rocks, on the Nigerian side of the border, is of the order of 300 km2 (see also Mounio occurrence - Niger No. 121-00-023). The granites, the most extensive and numerous outcrops of which are clustered around Matsena, are all arfvedsonite-bearing with aegirine and sometimes aenigmatite or astrophyllite. Turner (1974) distinguished six petrographic varieties that he considered probably represented distinct intrusions. Other minerals identified include hedenbergite, a calcic amphibole, probably hornblende, amblygonite, zircon, fluorite, allanite and pyrochlore. About 25 km east of Matsena occur a group of hills of volcanic rocks that are rhyolitic and mainly tuffs. The tuffs are generally very fine-grained but in some welded pumice fragments and pieces of rhyolite are present. A more homogeneous rhyolite contains phenocrysts of arfvedsonite, aegirine and aenigmatite in a matrix of quartz and feldspar with a little astrophyllite and spongy crystals of fluorite. In the northern part of the area are outcrops of a granite porphyry the aligned distribution of some of the outcrops suggesting they may be part of a ring-dyke. They contain quartz and perthite phenocrysts with poikilitic amphibole plates zoned from hornblende cores to arfvedsonite rims and aegirine rimmed by arfvedsonite in a groundmass of feldspar and quartz.