Mivula

Mivula is a ridge the greater part of which consists of coarse sodalite syenite, but the extent of the ridge is not given in the principal reference (Newton, 1959). The southern end of the ridge consists of Karoo sedimentary rocks but their relationship with the syenites is not clear; it may be a faulted one. The syenite consists of microcline perthite prisms up to 2.5 cm long with rare albite, abundant interstitial sodalite containing numerous inclusions of zeolite and cancrinite, brown biotite, cancrinite, which is described as rimming feldspar (?nepheline), opaque minerals and titanite. On the summit of the ridge a small area of darker rock occurs which contains about 30% biotite and amphibole, which may be arfvedsonite, microcline perthite, quartz, hexagonal pseudomorphs of alkali feldspar and phlogopite, which may be after nepheline, and remnant cores of a pale green pyroxene. A 15 m broad zone traversing the hill consists of fine-grained nepheline syenite of 50-60% microcline, 20-30% nepheline and 10-15% amphibole and biotite, the former probably being arfvedsonite. A pegmatite in one area consists solely of fibrous ferro-richterite which is described, with an analysis, by Newton and Drysdall (1960).