Rhomb porphyry

Rhomb porphyr is a volcanic rock with yellow-gray large porpyric rhomb shaped phenocrysts enbedded in a very fine grained red-brown matrix. The composistion of rhomb porphyr place it in the trachyte - latite classification of the QAPF diagram. Rhomb porphyr lavas are known only from three rift areas: The East African rift (including Mount Kilimanjaro), Mont Erebus near the Ross Sea in Antarctica and the Oslo rift in Norway.