Rocks and the Rock Cycle
Lecture Goals:
A) Types of Rocks
B) Igneous Rocks
C) Sedimentary Rocks
D) Metamorphic Rocks
E) The Rock Cycle
A) Types of Rocks
If we haven’t already done so, we will even tually be talking about the chemistry of minerals. By
then, you will learn that minerals are naturally occurring, inorganic, crystalline solids with
unique chemical compositi ons. We also need to define rocks. Rocks are naturally occurring
solids containing more than one mineral. As it turns out, some times rocks will contain only one
mineral. An example of this is a quartz sandstone . The only mineral it contains is quartz, but as
many separate grains rathe r than a single cry stal. So perhaps the definition of a rock needs to be
refined just a bit:
Rocks are naturally occurring solids containing one or more minerals.
Geologists recognize three broad groups of rocks:
1) Igneous Rocks (literal translati on: born from
fire): These are rocks that were formed from
originally molten states (see lava fountain, right)
2) Sedimentary Rocks: These are rocks that were
formed initially through the accum ulation of
sediment (e.g.,
particles of old
rock and minerals; see image of Mississippi Delta to right), or
new minerals formed through the result of chemical
precipitation or organic activity).
3) Metamorphic Rocks: Pre-existing rocks that are affect ed
by pressure, substantial changes in temperature or b y
chemically active fluids (e.g., hot water), can be altered.
These are the processes of metamorphism which can result
in minerals or fabric changes to rocks.
Over the course of GY 111, we will spend a lot of tim e
discussing the details of each of these rock groups, but some basic understanding of each of these
rocks is necessary now before we get into the rock cycle.
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