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Fun Facts About Volcano Rocks

Fun facts about volcano rocks start with their name and composition. Volcanic rocks can be either “intrusive,” in which they remain below the Earth’s crust, or they can be “extrusive,” wherein they surface above. Did you know that the same lava can produce vastly different volcanic rocks?

Volcano rocks are classified as “igneous” rocks and are the third most abundant rock on Earth, trailing only sedimentary and metamorphic rock. Basalt, pumice, and obsidian glass are all examples of extrusive volcanic rock; and an astounding 90% of the Earth’s crust is comprised of igneous rock. A layer of sedimentary rock covers most of it.

Fun Facts About Volcano Rocks

More Fun Facts About Volcano Rocks

Speaking of 90%, about 90% of the world’s active volcanoes are found in the Pacific region known as the Ring of Fire. Yet volcanoes are found throughout the planet and in fact, the oldest volcanic rock to date was found in Northern Quebec in Canada.

At the turn of the 21st century, geologists uncovered ancient volcanic rock in the Porpoise Cove. They initially thought the rock dated 2.8 billion years. However, further analysis revealed that the rock was closer to 4 billion years old, placing it around the time Earth was forming. This rare find truly encapsulates the importance of volcanic rock: what it can tell geologists about the planet and its mysterious past.

It’s true that all rock holds some answers, but igneous rock is especially helpful as it comes from within the planet. It is also dynamic, changing its composition depending on the environment in which it is extruded.

For example, the same felsic lava can be smooth obsidian glass in one climate (cool) and spongy pumice in another. The combination of air, gas, and temperature is unique to the formation of all volcanic rock. In total, over 700 different volcano rocks have been identified. Each one, unique.

Types of Volcano Rocks

As said, over 700 types of volcanic rock have been identified. The most common is basalt, which has a mafic composition – meaning it’s rich in magnesium and iron. Under the umbrella of “basalt” are adakite, hawaiite, icelandite, and picrite. Basalt is grey to black in color, with a fine-grained texture due to its rapid cooling process.

Indeed, the rate at which magma cools is one of the fascinating fun facts about volcano rocks. Does the extruded rock have time to create bubbles that will ultimately turn into cavities for a vesicular appearance? In the case of hyaloclastite and obsidian, the magma is cooled so quickly, it leaves little time for any crystal growth to occur.

Another common volcanic rock is basanite, which is extremely fine-grained. Rhyolite is another “felsic” volcanic rock and contains two main types: comendite and pantellerite, the latter of which has a higher iron and lower aluminum composition.

What’s In a Name?

Finally, did you know that intrusive volcanic rock, also known as “plutonic,” is named after the Roman god of the underworld Pluto? Similarly, extrusive volcanic rock, generally known as “volcanic rock,” takes its name from the Roman god of fire Vulcan. As for the term “igneous,” its Latin root tells you all you need to know about how volcanic rock is formed (from magma). The word is derived from “ignis,” which poetically means “born of fire.”