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Basalt is the most common volcanic rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands, including Iceland, the Faroe Islands, Réunion and the islands of Hawaiʻi.
Basalt is usually grey to black in color, but rapidly weathers to brown or rust-red due to oxidation of its iron-rich minerals into hematite and other iron oxides and hydroxides.
Basalt with a vesicular texture is called vesicular basalt, when the bulk of the rock is mostly solid (when the vesicles are over half the volume of a specimen, it is called scoria). This texture forms when dissolved gases come out of solution and form bubbles as the magma decompresses as it reaches the surface.