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SCI 245 Igneous Rocks CP WK 4

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Igneous rocks originate from magma where they have solidied.
When magma ows near the surface of the Earth, it forms into lava.
While the lava cools, rocks are formed, which are igneous rocks.
There are also rocks that do not reach the surface of the Earth,
which are called plutonic rocks that are also other types of igneous
rocks. The two categories of igneous rocks extrusive and intrusive.
Extrusive rocks are called this because they have been extruded and
came out of the Earth. Intrusive rocks are intruded, therefore they
stay inside the Earth. The magma of intrusive rocks hardens and
cools inside the Earth, beneath the surface; while the extrusive
rocks are the opposite, and cool on the outside of the Earth's
surface. The texture of the two categories of rocks is the most
distinguishable characteristic between the two. Intrusive rocks allow
a longer cooling time, while the crystals grow larger, giving the
intrusive rocks a coarse texture. Extrusive igneous rock forms when
molten rock reaches the earth's surface and cools. Air and moisture
cool the lava rapidly. Thus, extrusive rocks cool very quickly and
form small crystals, allowing the texture of the rock to become more
smooth than intrusive rocks.

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