Accessory minerals in nephelinite of Fernando-de Naronha  island (Brasil).

Kogarko L.N., Uvarova U, Sokolova E.V.,owthorn F., Otollini L, Grice J.

Vernadsky Inst, Moscow, University Monitoba Canada, Univ Ferrara Italia, Canadian Museum of Nature, Ottava

 

Almeida (1955) distinguished three periods of volcanic activity on Fernando de Naronha Island and three corresponding formations: 1 - the Remedius Formation, 2 - the Quixaba Formation and 3 - the Sao Jose Formation.

Olivine nephelinites of Quixaba Formation were investigated petrografically and geochemically.

The principal minerals of the olivine nephelinites are olivine,clinopyroxene, Fe-Ti oxide, nepheline. Accessory minerals are calcite, apatite, K-feldspar and highBa mica. Investigation of the composition and crystallographic structure of Ba-rich mica showed that this mica represents a new mineral -oxykinoshitalite which is bright orange to brownish and occurs as small irregularly shaped interstitial crystals 0.03-0.05 mm in diameter.