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Pictures of Igneous Rocks

Photos and Descriptions of Common Intrusive and Extrusive Igneous Rock Types

Commodity by: , PhD, RPG

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 well-nigh ii inches (five centimeters) beyond.

What are Igneous Rocks?

Igneous rocks are formed from the solidification of molten stone material. Some form below Earth'southward surface. Some form on or above World's surface. We draw these 2 basic types:

Intrusive igneous rocks crystallize below Earth's surface, and the slow cooling that occurs in that location allows large crystals to form. Examples of intrusive igneous rocks are: diabase, diorite, gabbro, granite, pegmatite, and peridotite.

Extrusive igneous rocks erupt onto the surface, where they cool quickly to form pocket-size crystals. Some cool so chop-chop that they form an amorphous drinking glass. These rocks include: andesite, basalt, dacite, obsidian, pumice, rhyolite, scoria, and tuff.

Pictures and brief descriptions of some common igneous rock types are shown on this page.

Dacite is a fine-grained, extrusive igneous rock that is usually light in color. It has a composition that is intermediate between rhyolite and andesite. The specimen shown is nigh four inches (x centimeters) across.

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

Diabase is an intrusive igneous rock composed mostly of plagioclase feldspar and pyroxene minerals. The grains in diabase are larger than those in basalt but smaller than those in gabbro. Diabase is used in the structure industry every bit trap rock or dimension stone. When the diabase contains colorful labradorite crystals, it makes an especially overnice architectural stone.

Gabbro is a fibroid-grained, dark-colored, intrusive igneous rock that contains feldspar, pyroxene, and sometimes olivine. The specimen shown above is well-nigh ii inches (five centimeters) across.

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

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

Granite is a coarse-grained, light-colored, intrusive igneous rock that contains mainly quartz, feldspar, and mica minerals. The specimen to a higher place is most two inches (five centimeters) beyond.

Peridotite is a coarse-grained intrusive igneous stone that is equanimous nearly entirely of olivine. It may contain small amounts of amphibole, feldspar, quartz, or pyroxene. The specimen shown above is nigh ii inches (five centimeters) across.

Pegmatite is a calorie-free-colored, extremely fibroid-grained intrusive igneous rock. It forms nigh the margins of a magma sleeping accommodation during the final phases of magma chamber crystallization. It oft contains rare minerals that are not found in other parts of the magma chamber. The specimen shown above is about two inches (5 centimeters) across.

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) beyond.

Pumice is a calorie-free-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 in a higher place is about two inches (v centimeters) beyond.

Scoria is a nighttime-colored, vesicular, extrusive igneous rock. The vesicles are a result of trapped gas within the melt at the time of solidification. Information technology often forms equally a frothy chaff 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 (5 centimeters) across.

Fire Opal is sometimes institute filling cavities in rhyolite. Long after the rhyolite has cooled, silica-rich ground water moves through the rock, sometimes depositing gems similar opal, red beryl, topaz, jasper, or agate in the cavities of the rock. This is one of many first-class geological photographs generously shared through a Creative Commons License by Didier Descouens.

Unakite is a colorful rock composed of green epidote and pink orthoclase. Information technology is formed when granite, an igneous stone, is metamorphosed by hydrothermal activeness. Attractive pieces of unakite are often used to brand cabochons, tumbled stones, pocket-sized sculptures, and other lapidary items. Information technology is named afterwards the Unaka Mountains of eastern Tennessee.

"Trap Rock" is a layman'southward term for any nighttime-colored igneous stone that is used to make crushed rock. This crushed stone tin be used equally road base material, or as an amass in concrete or asphalt. The well-nigh common types of trap rock are basalt, diabase, gabbro, and peridotite. Epitome copyright iStockphoto / Brilt.

The best way to learn about rocks is to have a collection of specimens to examine while you study. Seeing and handling the rocks will assist y'all understand their limerick and texture much ameliorate than reading about them on a website or in a volume. The Geology.com store offers inexpensive rock collections that can be mailed anywhere in the The states or U.Southward. Territories. Mineral collections and instructive books are also available.

Welded Tuff is a stone that is composed of materials that were ejected from a volcano, fell to World, and then lithified into a rock. It is normally composed mainly of volcanic ash and sometimes contains larger size particles such as cinders. The specimen shown above is most two inches (five centimeters) across.

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