Basalt is a common extrusive volcanic rock. It is usually gray to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or gray. The most common uses for this rock are as aggregate in highway construction, railroad ballast, and tile. Basalt is also a major component of asphalt pavement. On Earth, most basalt magmas have formed by decompression melting of the mantle. Basalt has also formed on Earth's Moon, on Mars, Venus, and even on the asteroid Vesta. Source rocks for the partial melts probably include both peridotite and pyroxenite. The crustal portions of oceanic lithospheric plates are composed predominantly of basalt, produced from upwelling mantle below ocean ridges. 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 are generally referred to as dolerite (also called diabase) or gabbro.
Photographed by Michael P. Klimetz
[Porphyritic]
Valmont
COLORADO
Photographed by Michael P. Klimetz
[Copper-Bearing]
Houghton
MICHIGAN
Photographed by Michael P. Klimetz
Chimney Rock
Somerset County
NEW JERSEY
Photographed by Michael P. Klimetz
[Amygdaloidal]
OREGON
Photographed by Michael P. Klimetz
[Vesicular]
TAHITI
Photographed by Michael P. Klimetz
[Porphyritic Olivine Basalt]
REUNION ISLAND
Photographed by Michael P. Klimetz
[Porphyritic Olivine Basalt]
HAWAII
Photographed by Michael P. Klimetz
Archean
[3.6 Ga]
Komati River
Barberton Greenstone Belt
SOUTH AFRICA
Photographed by Michael P. Klimetz
Archean
[3.6 Ga]
Komati River
Barberton Greenstone Belt
SOUTH AFRICA
Photographed by Michael P. Klimetz
SPITZBERGEN
Photographed by Michael P. Klimetz
Panamint Range
CALIFORNIA
Photographed by Michael P. Klimetz
Snake River Plain
IDAHO
Photographed by Michael P. Klimetz
PUERTO RICO
Photographed by Michael P. Klimetz
[Porphyritic]
Cerro Negro
NICARAGUA
Photographed by Michael P. Klimetz
[Porphyritic]
Robler Formation
PUERTO RICO
Photographed by Michael P. Klimetz
PUERTO RICO
Photographed by Michael P. Klimetz
Mount Kenya
KENYA
Photographed by Michael P. Klimetz
Deccan Plateau
INDIA
Photographed by Michael P. Klimetz
[Vesicular Olivine Basalt]
AMERICAN SAMOA
Photographed by Michael P. Klimetz
[Porphyritic Bytownite Basalt]
Linewath Bridge
Cumbria
UNITED KINGDOM
Photographed by Michael P. Klimetz
[Porphyritic Bytownite Basalt]
Linewath Bridge
Cumbria
UNITED KINGDOM
Photographed by Michael P. Klimetz
[Vesicular and Hematite-Stained Alkaline Basalt]
Carboniferous
Arthur's Seat
Edinburgh
SCOTLAND
Photographed by Michael P. Klimetz
[Vesicular and Hematite-Stained Alkaline Basalt]
Carboniferous
Arthur's Seat
Edinburgh
SCOTLAND
Photographed by Michael P. Klimetz
[Vesicular and Hematite-Stained Alkaline Basalt]
Carboniferous
Arthur's Seat
Edinburgh
SCOTLAND
Photographed by Michael P. Klimetz
[Vesicular and Amygdular Tholeitic Basalt]
Tertiary
Cuillen
Isle of Skye
SCOTLAND
Photographed by Michael P. Klimetz
[Vesicular and Amygdular Basalt]
Miocene-Pliocene
Henderson
Clark County
NEVADA
Photographed by Michael P. Klimetz
[Vesicular and Amygdular Basalt]
Miocene-Pliocene
Henderson
Clark County
NEVADA
Photographed by Michael P. Klimetz
[Vesicular and Amygdular Basalt]
Miocene-Pliocene
Henderson
Clark County
NEVADA
Photographed by Michael P. Klimetz
[Vesicular and Amygdular Basalt]
Miocene-Pliocene
Henderson
Clark County
NEVADA
Photographed by Michael P. Klimetz
Talcott Basalt
Jurassic
Tilcon Quarry
I-84
Plainville
Hartford County
CONNECTICUT
Photographed by Michael P. Klimetz
Talcott Basalt
Jurassic
Tilcon Quarry
I-84
Plainville
Hartford County
CONNECTICUT
Photographed by Michael P. Klimetz
Talcott Basalt
Jurassic
Tilcon Quarry
I-84
Plainville
Hartford County
CONNECTICUT
Photographed by Michael P. Klimetz
Spherulitic and Porphyritic Alkaline Basalt
Tertiary to Recent
AZORES
Photographed by Michael P. Klimetz
Spherulitic and Porphyritic Alkaline Basalt
Tertiary to Recent
AZORES
Photographed by Michael P. Klimetz
Spherulitic and Porphyritic Alkaline Basalt
Tertiary to Recent
AZORES
Photographed by Michael P. Klimetz
Amygdaloidal Vesicular Basalt
Tertiary to Recent
Burns
Harney County
OREGON
Photographed by Michael P. Klimetz
Amygdaloidal Vesicular Basalt
Tertiary to Recent
Burns
Harney County
OREGON
Photographed by Michael P. Klimetz
Amygdaloidal Tholeiitic Basalt
Tertiary
Cuillin
Isle of Skye
SCOTLAND
Photographed by Michael P. Klimetz
Amygdaloidal Tholeiitic Basalt
Tertiary
Cuillin
Isle of Skye
SCOTLAND
