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Basalt: Grand Manan Island

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Double image of a long gray rock with paper label ‘columnar basalt’ and a side view of the same
Basalt: Grand Manan Island. Triassic. Grand Manan Island, New Brunswick. Collector: A. Gesner (?), c. 1840. New Brunswick Museum (NBMR 1273). Image width (left) 26 cm; Specimen width (right) 10 cm. Basalt is an extrusive volcanic rock that erupts at the surface. Columnar basalts are formed when the thick lava flow cools and contracts forming joints of fractures.