While there are over 700 different kinds of igneous rocks, they all started as molten rock called magma. If they all started as the same stuff, why are there so many different kinds?
- Magma underground cools much slower than lava does on the surface. Magma that cools slowly tends to form large crystals. Lava that cools quickly tends to form tiny crystals or glass with no crystals at all.
- Different magmas form by the melting of different rocks, so they contain different chemicals. Melted granite will have different chemicals from melted sandstone. Those chemicals determine which minerals will be in the new igneous rock when the magma cools.
- Magmas vary in temperature. Some magmas are hotter than 1300°C/2400°F, while others may be cooler than 700°C/1300°F. Hotter magmas may melt some of the rock around them, adding to their chemical content. With cooler magmas, some of the minerals may have already crystallized and settled out.
- Identifying Igneous Rocks
A basic chart to get you started with identifying igneous rocks. - Intrusive and Extrusive Rocks
Understanding the difference between magma and lava helps you understand why some igneous rocks have large or small crystals. - Igneous Sugar.
A fun, easy, tasty way to explore intrusive and extrusive rocks. - Light and Dark Minerals
Melting point is another important part of identifying minerals. Luckily, the color of the rock usually makes this fairly easy. - Igneous Rocks and Bubbles
The next time you drink a carbonated soda, think about pumice and other igneous rocks with bubbles. - Mystery of the Golden Needles
Can you solve the Mystery of the Golden Needles?
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