Download Chapter 6: Rocks

Chapter 6: Rock Cycle
Unlike minerals that are classified by what element makes them up, rocks are classified
according to the processes that form them.
There are only 3 basic types of rocks: 
1.
Igneous Rocks: formed by the cooling & hardening of hot, molten rock.
magma (inside Earth) or lava (outside Earth)
2.
Sedimentary Rocks: formed by the compaction & cementation of layers of
sediment.
 Sediments are materials such as rock fragments, plant or animal remains,
or minerals that settle out of solution onto lake & ocean bottoms.
Metamorphic Rocks: formed from other rocks that are affected by heat &
pressure. (Enormous heat & pressure)
3.
Since rocks form from other rocks over & over again, we might see how they are related
through the rock cycle.
Cycles really have no beginning or end = continuum
However, there is a point in the rock cycle that the rocks & minerals are really in a dissolved
liquid form that we call magma or lava. (It makes a “beginning.”) The rock cycle is nothing
more than a ‘map’ or model of the processes that rocks undergo.
1.
The Rock Cycle:
The liquid lava/magma would have to cool & solidify to become a solid rock.
= the process is – solidification
Once solid it is called Igneous Rock.
Three things can happen to igneous rock once it is formed:
a. melt and turn into magma / lava again
b. break apart by weathering & erosion making sediments
c. heat & pressure can change (metamorphose) the rock
------------------------------------------------------------------------------------------------------------------------2. Sediments will deposit & form layer after layer; the older on the bottom and the younger
on top. The older layers get squeezed or compacted together making “nature’s cement”
or Sedimentary rocks.
Three things can happen to sedimentary rock once it is
formed:
a. melt and turn into magma / lava again
b. break apart by weathering & erosion making sediments
c. heat & pressure can change (metamorphose) the rock
------------------------------------------------------------------------------------------------------------------------3. Rocks that were already formed but undergo enormous heat & pressure are changed
into another rock. “Metamorphose” means change. A changed rock is a Metamorphic
rock. Rocks can be changed deep below the crust or when mountains are being
formed.
Three things can happen to metamorphic rock once it is formed:
d. melt and turn into magma / lava again
e. break apart by weathering & erosion making sediments
f. heat & pressure can re-change or (metamorphose) the rock again.
It's not hard to see that this metamorphic
rock, called gneiss, has been intensely
folded! This rock had to have been under
very high pressure and temperature to
allow it to fold like this without breaking.