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Igneous Rocks
Granite
Rhyolite
Diorite
Andesite
Obsidian
Pegmatite
Pumice
Scoria
Tuff
Gabbro
Basalt
Peridotite
Granite
Granite is a coarse-grained, light colored, intrusive igneous rock
that contains mainly quartz and feldspar minerals. The
specimen above is about two inches.
Granite
Granite is a light-colored igneous rock with
grains large enough to be visible with the
unaided eye. It forms from the slow
crystallization of magma below Earth’s
surface. Granite is composed mainly of quartz
and feldspar with minor amounts of micas,
amphiboles and other minerals. This mineral
composition usually gives granite a red, pink,
gray or white color with dark mineral grains
visible throughout the rock.
Granite
Granite is the best-known igneous rock. Many people recognize
granite because it is the most common igneous rock found at
Earth's surface and because granite is used to make many objects
that we encounter in daily life. These include counter tops, floor
tiles, paving stone, curbing, stair treads, building veneer and
cemetery monuments.
Granite is also well-known from its many world-famous natural
exposures. These include: Stone Mountain, Georgia; Yosemite
Valley, California, Mount Rushmore, South Dakota; Pike's Peak,
Colorado; and White Mountains, New Hampshire.
Granite
Granite
Rhyolite
Rhyolite is a light-colored, fine-grained, extrusive igneous rock
that typically contains quartz and feldspar minerals.
Diorite
Diorite is a coarse-grained, intrusive igneous rock that contains a
mixture of feldspar, pyroxene, hornblende and sometimes quartz.
Andesite
Andesite is a fine-grained, extrusive igneous rock composed
mainly of plagioclase with other minerals such as hornblende,
pyroxene and biotite.
Gabbro
Gabbro is a coarse-grained, dark-colored, intrusive igneous rock.
It is usually black or dark green in color and composed mainly of
the minerals plagioclase and augite. It is the most abundant rock
in the deep oceanic crust.
Basalt
Basalt is a fine-grained, dark-colored extrusive igneous rock
composed mainly of plagioclase and pyroxene.
Basalt
Basalt is a dark-colored, fine-grained, igneous rock composed
mainly of plagioclase and pyroxene minerals. It most commonly
forms as an extrusive rock, such as a lava flow, but can also form in
small intrusive bodies, such as an igneous dike or a thin sill. It has a
composition similar to gabbro. The difference between basalt and
gabbro is that basalt is a fine-grained rock while gabbro is a coarsegrained rock.
Earth's Most Abundant Bedrock
Basalt underlies more of Earth's surface than any other rock type.
Most areas within Earth's ocean basins are underlain by basalt.
Although basalt is much less common on continents, lava flows
and flood basalts underlie several percent of Earth's land surface.
Basalt is a very important rock.
Peridotite
Peridotite is a coarse-grained intrusive igneous rock that is
composed almost entirely of olivine. It may contain small
amounts of amphibole, feldspar, quartz or pyroxene.
Pegmatite
Pegmatite is a light-colored, extremely coarse-grained intrusive igneous
rock. It forms near the margins of a magma chamber during the final
phases of magma chamber crystallization. It often contains rare minerals
that are not found in other parts of the magma chamber.
Obsidian
Obsidian is an igneous rock that forms when molten rock
material cools so rapidly that atoms are unable to arrange
themselves into a crystalline structure. The result is a volcanic
glass with a smooth uniform texture that breaks with a
conchoidal fracture.
Pumice
Pumice is a light-colored vesicular igneous rock. It forms through
very rapid solidification of a melt. The vesicular texture is a result
of gas trapped in the melt at the time of solidification.
Scoria
Scoria is a dark-colored, vesicular, extrusive igneous rock. The
vesicles are a result of trapped gas within the melt at the time of
solidification. It often forms as a frothy crust on the top of a lava
flow or as material ejected from a volcanic vent and solidifying
while airborne.
Tuff
Welded Tuff is a rock that is composed of materials that were
ejected from a volcano, fell to Earth, and then lithified into a
rock. It is usually composed mainly of volcanic ash and
sometimes contains larger size particles such as cinders.