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Important Facts About the Popular Igneous Rock

Igneous Rock Facts
A compilation of igneous rock facts, which shed light on some little-known attributes of this rock type. As you go through these facts, you will realize why igneous rocks are so popular in numerous fields including construction and jewelry making.
Abhijit Naik
Last Updated: Feb 20, 2018
Approximately 90 percent of the Earth's upper crust is made up of igneous rocks. These rocks are found in abundance all over the planet, but the fact that they are covered by a layer of sedimentary rocks means we don't get to see them until we hit the igneous rock bed.
Facts about Igneous Rocks
Igneous rocks are formed when magma (molten rock) cools and solidifies, either on the surface of the Earth, or beneath the Earth's crust. Depending on where their formation takes place, igneous rocks are categorized into two groups -- extrusive igneous rocks and intrusive igneous rocks.
Extrusive and intrusive igneous rocks
When magma comes to the surface of the Earth as a result of some volcanic activity and solidifies to become a rock, this rock is referred to as an extrusive igneous rock. On the other hand, when magma seeps in between the layers of sedimentary rocks beneath the crust and solidifies to form a rock, it is referred to as an intrusive igneous rock.
The term 'igneous' is derived from the Latin word 'ignis', meaning 'of fire'. Extrusive rocks are also known as volcanic rocks after the Roman god of fire -- Vulcan, while intrusive rocks are also known as Plutonic rocks after the Roman god of the underworld -- Pluto.
Igneous rocks are also called 'Fire rocks' as they are closely associated with volcanic activity. The magma, or lava that it is referred to as when it comes to the surface, is produced when the pre-existing rocks beneath the Earth's crust melt as a result of rise in temperature, fall in pressure, or the combination of these two factors.
As of today, around 900 different types of igneous rocks have been identified; most popular among these are basalt, granite, andesite, diorite, pumice, obsidian, and gabbro. These rocks are classified on the basis of following factors:
» Chemical composition of magma
» Temperature at which solidification occurs
» Speed at which cooling takes place
The most prominent characteristics of igneous rocks are their color and the size of the crystals formed in them. Their color usually varies from pink to black, depending on the mineral content of the rock in question. In these rocks, the crystals of varying size are interlocked into each other; this gives stability to the rock structure. These rocks are strong, heat-resistant, less radioactive, and are found in abundance on the planet.
Basalt Rock
Basalt (extrusive rock) and granite (intrusive rock) are two of the most common igneous rock types on the Earth, and cover most of the igneous deposits on the planet. Usually, the rocks in deep ocean floors are known to be basaltic in nature, while the rocks in the continental mass are granitic in nature.
Owing to their interlocked crystals, igneous rocks boast of a strong and stable structure, which, in turn, makes them highly popular in the world of architecture. Each igneous rock variety has uses of its own; some are used for kitchen counters, some for decorative purpose, and some for interior designing and jewelry making.
Igneous rocks have been used in architectural construction for several centuries. In fact, some of the most famous monuments in the world have been built using these rocks and therefore, it would be a bit harsh on our part to ignore these monuments when compiling interesting facts about this rock type.
Igneous Rocks - Architectural Marvels
Mount Rushmore
Mount Rushmore (USA)
Basalt, trachyte, and scoria
Moai Statues
Moai Statues (Easter Island)
Stonehenge (England)
Vietnam Veterans Memorial
Vietnam Veterans Memorial (USA)
Other than the man-made structures enlisted above, there also exist some natural wonders of the world which were formed when igneous rocks in the said region were exposed to agents of erosion, like water and wind. Of these, the Giant's Causeway and the Pulpit Rock (a.k.a. Preikestolen) seem to be the most famous.
Igneous Rocks - Natural Wonders
Giant's Causeway
Giant's Causeway (Ireland)
Pulpit Rock
Pulpit Rock (Norway)
Some of the most prominent examples in North America include the Half Dome in Yosemite National Park, Ruth Gorge in Alaska, and the Bugaboos range in neighboring country of Canada. Even the islands of Hawaii are largely made up of basalt, which is again a type of igneous rock.
From construction of buildings to interior designing, igneous rocks are used everywhere, and their characteristic features play a crucial role in their immense popularity. Igneous rock identification may seem pretty difficult, but once you get the basics right, you will be able to do it quite easily. Other than the texture and color, the place where you find the rock specimen also plays a vital role in the identification process.
Lava Rock Closeup
Basalt Lava Rock
Obsidian Volcanic Glass
Lava stone
Diorite Igneous Rocks