The Island of Margarita, Venezuela, is largely composed of crystalline rocks, mainly garnetiferous and graphitic schist and gneiss, greenstone and amphibolite, intruded by peridotite and serpentinite. A belt of graphitic sericite schist with interbedded marble lies south and east of the higher-grade metamorphics. Small bodies of pyroxene diorite or gabbro intrude the sericite schist. The large mass of coarse-grained soda granite porphyry forming Cerro Mata Siete is believed to underlie the sericite schist unconformably. For the most part the metamorphics strike northeast and dip steeply southeast.
Along the south and southeast margin of the island Eocene sandstone, shale, and conglomerate are folded in a general synclinal structure and overlain unconformably by patches of gently dipping Miocene sediments. Pebbles and cobbles of volcanic rocks are abundant in the lower beds of the Eocene section, though no source for such rocks is known on the island.
Major deformation and metamorphism in Margarita presumably occurred before the end of the Cretaceous, with renewed folding after the Eocene sediments were deposited and prior to the Miocene.