Igneous Rocks Examples

Rocks are generally separated into one of three different categories: igneous, sedimentary, and metamorphic. The word igneous means that the rock became a solid after having originally been hot magma, or lava. These rocks are formed from the molten material found beneath the Earth's crust.

Therefore, igneous rocks have a few similar characteristics and can often be easily identified by students who know what to look for. They are typically very strong because they were formed when minerals melted together and then cooled, basically super-gluing the rock together. Since they're formed from primarily minerals, they're usually white, gray, or black rocks. If they do have other colors, those colors are usually really pale. Finally, they're texture usually looks like something that has been baked in a really hot oven, because they were! There are often holes where gas bubbles were formed then released by the heat of the magma, and they're usually very coarse-looking.

Igneous rock is usually found at three different types of locations: along the places where the Earth's tectonic plates meet, in the places where these plates pull away from each other (such as along the ridges in the ocean) and in places where the land masses have pushed together, like the mountains.

1. Pumice Stone

Pumice stone is found near the site of a volcanic eruption which sent rock and molten lava to the surface. Gas bubbles in the rock "popped" from the extreme temperature shift when the lava cooled, leaving a stone that resembles a sponge. This lightweight, airy rock is often ground up and used as an abrasive in soaps and household cleaners, as well as for industrial purposes. When left intact, larger chunks of the stone are used for scrubbing everything from dead skin cells to industrial compounds.

2. Granite

Granite is one of the most common rocks on Earth, and is the most common igneous rock. This dense stone is used in construction, for everything from basic building to beautiful polished countertops. Because the minerals in the granite crystalized as it cooled, granite often has sparkly flakes embedded in it.

3. Obsidian

Most igneous rock forms below the Earth's surface, but one rock-obsidian, or volcanic glass-forms above the surface. This jet-black glass is actually cooled lava, and due to the way that obsidian breaks, its edges are incredibly sharp. That's why many native cultures and ancient peoples have relied on obsidian gathered from volcanic eruptions to make arrow heads, weapons, household knives, and more. Even today some surgical instruments are made from obsidian-tipped tools due to the sharpness of the newly formed blade.