That's right! This rock was born in a volcano! It started out as hot lava erupting from a volcano. Filled with gases, the rock cooled very quicklyso quickly that the gases didn't have time to escape. Instead, they were trapped in bubbles inside the rockthe same bubbles that now make the rock float!
This rock is called pumice. It is an igneous rock, just like all rocks formed from magma. Magma is molten rock that rises up from the earth's mantle deep underground! Magma can solidify in many different ways, so there are many kinds of igneous rock:
Like pumice, obsidian is made of cooled lava. But because it flowed out of the volcano like a river, it's very dense. The lava cooled so quickly that crystals did not have time to form, so obsidian is actually a kind of glass! Its sharp edges have led many people of the past to make tools and weapons from it.
Basalt is the most common form of cooled lava. Basalt can form in widespread lava flows, and can be seen in many locations across the globe. In India, a gigantic basalt flow covers over 250,000 square miles.
Granite is made of magma that cooled while still deep underground. Many crystals formed as the magma cooled, so granite is speckled with mineral crystals like quartz, feldspar and mica.
|How are other rocks formed?|
You don't have to live near a volcano to find igneous rocks! Granite forms in underground magma chambers that are later exposed by the weather, so you can find it throughout the world. And ancient volcanoes may have left obsidian or pumice in your area.
Whenever you find an igneous rock, remember that you're holding a piece of the earth's mantlejust be glad it's had time to cool off!
Check with the nearest geological survey to find out where to look for igneous rocks near you!
Help me solve another geo-mystery!
© The Children's Museum of Indianapolis, 2000