This produces a volcanic arc, composed of mainly basalt, andesite and rhyolite. Elsewhere clasts of quartzite, limestone, sandstone, mudstone, jasper and basalt can be found. That magma crystallizes to mafic rocks such as gabbro and basalt. The region is known for stone quarrying to produce limestone, marl, marble, and basalt. Oceanic crust is composed primarily of basalt and gabbro. The island consists chiefly of basalt and lava. The mesa is topped by a hard volcanic basalt. Included within the Interior Plateau is a coalescing series of layered flood basalt lava flows. Continental rifting commonly follows flood basalt volcanism. Pyroxene and feldspar are the major minerals in basalt and gabbro. The southern part of the city rests on hardened basalt lava flows. Their dark tone is due to the volcanic rock called basalt. Flood basalt describes the formation in a series of lava basalt flows. The facies are named after the metamorphic rock formed under those facies conditions from basalt. Granites may absorb fragments of shale or pieces of basalt.