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Time to Rock Your World!
Chapter 4
Rock or Mineral:What’s the
Difference?
Which is a ROCK and
which is a MINERAL?
• There’s a big
difference! Minerals
are made of a
combination of elements
and rocks are made of a
combination of minerals
and organic matter
• Some of the more
common minerals found
in rocks are feldspar,
quartz, and mica
So How are Rocks Made?
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Many processes go into
making a rock. Probably the
most important item needed
to make a rock is TIME!!!
Some of the processes that
make a rock are:
Compaction
Cementation
Erosion
Weathering
Heat
Pressure
Melting
Cooling
This is a Rock’s Life
• All rocks begin as magma.
When the magma cools and
crystallizes, it becomes an
IGNEOUS rock.
• Weathering and erosion
break down the igneous rock
into SEDIMENTS, which
get compacted and
cemented together to form
a SEDIMENTARY rock.
• As the sedimentary rock
has heat and pressure
applied to it, it becomes a
METAMORPHIC rock.
• Over time, the metamorphic
rock re-melts, cools, and
the whole cycle starts again!
First Stop: Igneous Rocks
• The word igneous comes
from the Latin word
“ignis” which means FIRE!
• Igneous rocks are created
from the crystallization of
magma/lava
• Igneous rocks can be
classified based on
LOCATION (which tells
the texture) and
COMPOSITION (which
tells the color)
Location, Location, Location!
•
Basalt
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Pumice (it
actually floats
in water!)
•
Obsidian
When igneous rocks form from
the cooling of lava on the Earth’s
surface, we call them
EXTRUSIVE
Because of water and air, these
rocks cool very quickly
Sometimes the lava cools so fast
that gas bubbles get trapped or
crystals don’t form at all!
Terms to describe the texture
of extrusive igneous rocks are:
1. Glassy
2. Fine-grained (very small
crystals)
3. Vesicular (has holes where gas
bubbles were)
Location, cont’d
• Igneous rocks that form
from the crystallization of
magma BELOW the Earth’s
surface are called
INTRUSIVE
• Because water and air are
no longer a factor in the
cooling process, the magma
cools very slowly
• The mineral crystals are
large enough to see
without a magnifying glass,
which is described as
COARSE-GRAINED
texture
Granite
Diorite
Composition and Color
Obsidian
is MAFIC
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Granite is
INTERMEDIATE
Rhyolite is
FELSIC
•
What minerals a rock is made
of is called its
COMPOSITION
The color of the minerals will
indicate the color of the rock
3 groups based on color:
1.
Mafic: made of all dark colored,
dense minerals and form from
easily flowing lavas
2. Intermediate: made of 50% light
colored and 50% dark colored
minerals
3. Felsic: made of all light colored,
low density minerals and form
from thick, non-flowing lavas