Basalt
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 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