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Igneous Rocks


Pictures of Intrusive and Extrusive Igneous Rock Types



What are Igneous Rocks?



Igneous rocks are formed from the solidification of molten rock material. There are two basic types: 1) intrusive igneous rocks such as diorite, gabbro, granite and pegmatite that solidify below Earth's surface; and 2) extrusive igneous rocks such as andesite, basalt, obsidian, pumice, rhyolite and scoria that solidify on or above Earth's surface. Pictures and brief descriptions of some common igneous rock types are shown on this page.


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.

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.



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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. 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.

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.

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.

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.

IGNEOUS ROCKS
Andesite
Andesite
Basalt
Basalt
Quartz Diorite
Diorite
Gabbro
Gabbro
Granite
Granite
Obsidian
Obsidian
Pegmatite
Pegmatite
Peridotite
Peridotite
Pumice
Pumice

Rhyolite
Rhyolite

Scoria
Scoria

Welded Tuff
Tuff

METAMORPHIC ROCKS
Amphibolite
Amphibolite
Gneiss
Gneiss
Hornfels
Hornfels
Marble
Marble
Novaculite
Novaculite

Phyllite
Phyllite

Quartzite
Quartzite

Muscovite Schist
Schist

Slate
Slate

Soapstone
Soapstone

   
SEDIMENTARY ROCKS
Breccia
Breccia
Chert
Chert
Anthracite Coal
Coal
Conglomerate
Conglomerate
Dolomite
Dolomite
Flint
Flint
Hematite Iron Ore
Iron Ore
Limestone
Limestone
Oil sand
Oil Sand
Oil shale
Oil Shale
Halite Rock Salt
Rock Salt
Sandstone
Sandstone
Shale
Shale
Siltstone
Siltstone
   
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