Basalt

Basalt is a common gray to black volcanic rock. It is usually fine-grained due to rapid crystallization as lava on the Earth's surface. It may be porphyritic containing larger crystals in a fine matrix. Basalt in the tops of subaerial lava flows and cinder cones will often be highly vesiculated, imparting a lightweight "frothy" texture to the rock. The term basalt is at times applied to shallow intrusive rocks with a composition typical of basalt, but rocks of this composition with a phaneritic (coarse) groundmass should generally be referred to as diabase or gabbro. The crustal portions of oceanic tectonic plates are predominantly made of basalt.

References

• {{note|Hyndman85}} {{Book reference | Author=Hyndman, Donald W. | Title=Petrology of igneous and metamorphic rocks, 2nd ed.|Year=1985|Publisher=McGraw-Hill, Inc.|ID=ISBN 0-07-031658-9}}
• {{note|Blatt96}} {{Book reference | Author=Blatt, Harvey and Robert Tracy | Title=Petrology, 2nd ed. | Year=1996|Publisher=Freeman|ID=ISBN 0-7167-2438-3}}