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NOVA Online: Hot Rocks

Two kinds of igneous rock

Any rock that originates from the hot, melted—or molten—rock deep inside the earth is an igneous rock (the molten liquid is called magma when it's underneath the earth's surface, and lava when it's above ground.) The name igneous comes from the word ignis, which means "fire" in Latin.

  • Pumice is an example of extrusive igneous rock. The word extrusive means that the magma was forced onto the earth's surface and cooled in a matter of hours.


  • Granite is an example of intrusive igneous rock. Intrusive indicates that the magma was forced close to the surface, but then cooled more slowly underneath the surface.


How hot is lava?

When lava erupts from a volcano, it can be as much as 10 times hotter than boiling water! This is why you have to be very careful when you try to extract a piece of it to examine. pick ax in lava flow In this picture a geologist uses a pick ax to yank a piece of lava from the overflow.

Why
is it important to collect lava when it's still very hot?



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