Igneous Rock Types Menu Andesite Basalt Diorite Gabbro Granite Obsidian Pegmatite Peridotite Pumice Rhyolite Scoria Tuff

Andesite

Andesite is a fine-grained, extrusive igneous rock composed
mainly of plagioclase with other minerals such as hornblende, pyroxene
and biotite. The specimen shown is about two inches (five centimeters)
across.

Basalt

Basalt is a fine-grained, dark-colored extrusive igneous rock
composed mainly of plagioclase and pyroxene. The specimen shown is about
two inches (five centimeters) across.
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Diorite

Diorite is a coarse-grained, intrusive igneous rock that contains
a mixture of feldspar, pyroxene, hornblende and sometimes quartz. The
specimen shown above is about two inches (five centimeters) across.

Gabbro

Gabbro is a coarse-grained, dark colored, intrusive igneous rock
that contains feldspar, augite and sometimes olivine. The specimen shown
above is about two inches (five centimeters) across.

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 (five centimeters) across.

Obsidian

Obsidian is a dark-colored volcanic glass that forms from the
very rapid cooling of molten rock material. It cools so rapidly that
crystals do not form. The specimen shown above is about two inches (five
centimeters) across.

Pegmatitie

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. The
specimen shown above is about two inches (five centimeters) across.

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. The specimen shown above is
about two inches (five centimeters) across.

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. The
specimen shown above is about two inches (five centimeters) across.
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Rhyolite

Rhyolite is a light-colored, fine-grained, extrusive igneous rock
that typically contains quartz and feldspar minerals. The specimen
shown above is about two inches (five centimeters) across.
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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. The specimen shown above is about two inches (five
centimeters) across.
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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. The specimen shown above is
about two inches (five centimeters) across. Return to Top