Download Igneous Rock Reading

Igneous Rock Reading
Melting
The deeper in the crust you go, the hotter it gets. If you go deep enough into the crust, it is hot enough to melt rock. Rocks that are
pushed deep into the earth's crust will melt; this molten (melted) rock is called magma.
Because magma is very hot, it expands and fills in any spaces in the rock it can find. Sometimes magma never makes it to the
surface because there are not cracks in the crust to allow it to expand upwards. Sometimes the magma does find a crack in the
earth's crust and it makes its way all the way to the surface. Magma that reaches the surface creates a volcano.
NOTE: When magma comes out of the crust and onto the earth's surface it gets a new name: lava. Lava and
magma are the same thing: both are molten rock. But magma is the name for molten rock beneath the earth's
surface, and lava is the name for molten rock on the earth's surface.
Cooling and Solidifying
Whether it is on the earth's surface or underneath, the molten rock will eventually cool down. When it does, the magma or lava turns
back into a solid. The new rock that is formed when magma or lava cools is called and i gneous rock.
Minerals
When the original rock was melted, the minerals that made up the rock broke up into a liquid mush of elements that were no longer
structured at minerals (remember, part of being a mineral means it has to be solid). When magma or lava cools down and turns
back into a solid, however, new minerals form. That is why igneous rock is considered a brand new rock.
The size of mineral crystals is determined partly
by the amount of time the crystals have to grow.
The slower molten rock cools, the more time it
gives the minerals to grow.
When magma cools below the earth's surface,
the rock that is formed is called an intrusive
igneous rock. This magma cools much slower
than lava on the earth's surface, so it generally
has much larger mineral crystals that are often
clearly visible to the naked eye.
When magma cools above the earth's surface,
the rock that is formed is called an extrusive
igneous rock. This lava cools quickly because
the surface of the earth is much cooler than
deep in the crust. Because the lava cools
quickly, there is less time for mineral crystals to
grow large, so in general extrusive igneous
rocks have smaller crystals that usually can't be
seen with the naked eye.