What is the composition of an extrusive igneous rock?

Crystalline Extrusive Igneous Rocks These igneous rocks have textures composed of interlocking crystals, usually of varying mineral composition. Rhyolite, dacite, andesite, and basalt are crystalline extrusive igneous rocks form a continuum of composition from felsic to mafic and are presented in this order below.

What is the formation of igneous rocks?

Igneous rocks form when magma (molten rock) cools and crystallizes, either at volcanoes on the surface of the Earth or while the melted rock is still inside the crust. All magma develops underground, in the lower crust or upper mantle, because of the intense heat there.

What type of rock has interlocking crystals?

Igneous rocks
Igneous rocks are formed from molten rock called magma. They are mostly crystalline (made up of interlocking crystals) and usually very hard to break.

What is an example of an extrusive rock?

If the magma contains abundant volatile components which are released as free gas, then it may cool with large or small vesicles (bubble-shaped cavities) such as in pumice, scoria, or vesicular basalt. Other examples of extrusive rocks are rhyolite and andesite.

Is diorite extrusive igneous?

Diorite. Diorite is an intrusive igneous rock composed principally of the silicate minerals plagioclase feldspar (typically andesine), biotite, hornblende, and/or pyroxene. The chemical composition of diorite is intermediate between gabbro and granite.

Are metamorphic rocks interlocking or clastic?

Note that both rock types consist of interlocking crystals. to see other igneous features, click here. Metamorphic rocks consist of pre-existing (igneous, metamorphic, or sedimentary) rocks that underwent a change because of high temperatures and usually, pressure.

What are interlocking crystals?

Interlocking texture means that there is no space between individual crystals, because the crystals grew into one another. During cooling, crystals begin to form in the magma, much like ice crystals in a partially frozen drink.

Where do intrusive and plutonic igneous rocks form?

Dark colored diabase dikes intrude through light colored granite at Acadia National Park, Maine. NPS photo by Georgia Hybels. Intrusive, or plutonic, igneous rock forms when magma remains inside the Earth’s crust where it cools and solidifies in chambers within pre-existing rock.

How did the aphanitic rock get its name?

These fine-grained rocks are known as aphanitic —from a Greek word meaning “invisible.” They are given this name because the crystals that form within them are so small that they can be seen only with a microscope. If lava cools almost instantly, the rocks that form are glassy with no individual crystals, like obsidian.

How are phaneritic rocks similar to intrusive igneous rocks?

Phaneritic (phaner = visible) textures are typical of intrusive igneous rocks, these rocks crystallized slowly below Earth’s surface. As magma cools slowly the minerals have time to grow and form large crystals. The minerals in a phaneritic igneous rock are sufficiently large to see each individual crystal with the naked eye.

Where can I find igneous rocks in the United States?

Volcanic processes has shaped the extrusive igneous rock formations at these parks: Hawai’i Volcanoes National Park, Hawai’i [Geodiversity Atlas] [Park Home] Sunset Crater Volcano National Monument, Arizona [Geodiversity Atlas] [Park Home] Crater Lake National Park, Oregon [Geodiversity Atlas] [Park Home]