1. Minerals
Rocks
igneous
sedimentary
metamorphic
Minerals form rocks
Three rock types have different
properties because they form in unique
ways
Rock cycle interrelates all rocks
Environmental Geology
jbartlett@national.edu

2. 
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Naturally occurring
Inorganic
Solid element or compound
Definite chemical composition
Regular internal crystal structure
Identified by recognizing different physical properties
Figure 2.4B
Figure 2.4C

3. 
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The two fundamental characteristics
of a mineral are its chemical
composition and its crystal structure
Analyze the mineral composition
• Technology based
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Measure crystal structure and
symmetry
• Technology based
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Observe and measure physical and
special properties
• Easy for humans to see and recognize
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Color
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Hardness
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Cleavage
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Luster
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Density
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Form

4. Table 2.1

5. 
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A solid aggregate of one or more minerals, or mineral materials
Consists of many mineral grains or crystals forming a solid mass
Each rock contains a record of its own history
Three broad categories
• Igneous:
• Sedimentary:
• Metamorphic:
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cooled from melted magma
deposited from physical or chemical parts
altered from previous rocks
Three rock types each show a particular texture from the process of
formation
• Igneous:
• Sedimentary:
• Metamorphic:
Crystalline and interlocking
granular and layered
warped, banded or squeezed

6. Igneous Rocks
formed by the solidification and crystallization of a cooling magma
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Rocks formed from hot, molten rock material [magma]
Usually composed of silicate minerals + some dissolved gases
+ water
Plutonic rocks form if magma cools inside earth’s crust (does
not flow onto surface); coarse crystals will grow
Volcanic rocks form if magma flows onto surface as lava;
glass often forms
Coarse, visible crystals indicate time spent cooling = depth
underground
St Cloud Granite
St Cloud, MN
1.7 + billion years old

7. Igneous Rocks
Felsic
Intermediate
low iron
light toned
Mafic
high iron
dark toned
Volcanic:
Surface,
fine
grained
Rhyolite
Andesite
Basalt
Plutonic:
Deep,
coarse
grained
Granite
Diorite
Gabbro

8. •
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Sediments are accumulations of mineral or
rock particles produced by weathering of
pre-existing rocks and minerals
Sediments are eroded, transported, and
deposited and buried in many sedimentary
environments
Gravity and transport play a role in the
formation of all sedimentary rocks
Layering is a very common feature of
sedimentary rocks and is used to identify the
origins of sedimentary rocks
Sedimentary rocks are formed at or near the
earth’s surface and at temperatures close to
ordinary surface temperatures.
St Peter Sandstone
St Paul, MN
455 million years old

9. 
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“Changed form” rock
Rock formed from pre-existing rock or
minerals
Heat, pressure, and chemically active fluids
cause changes in rock
Heat increases as a rock is buried or is close
to magma – not quite melting but can have
big effect such as recrystallization
Pressure increases with burial or collision
between moving continents and can cause
deformation, recrystallization
Fluids become heated and circulate with
burial or with location near a magma
chamber
Morton Gneiss
Central MN
2.5 + billion years old

10. 
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Any kind of preexisting rock (another rock) can be
metamorphosed
Foliation: when a rock is subjected to directed stress, its
minerals form elongated/platy crystals and line up
parallel to each other
Metamorphic rocks without foliation do not show
directed stress
• Marble is metamorphosed limestone
• Quartzite is metamorphosed quartz-rich sandstone
Metamorphic rocks with foliation show directed stress or
pressure
• Slate – low grade foliated metamorphic rock
• Schist and Gneiss (nice) – high grade metamorphic
rocks

11. 
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Shows the
interrelationships among
the three rock types
Rocks of any type can be
transformed into rocks of
another type or into
another distinct rock of
the same general type
through the geologic
processes
Rocks are continually
being changed by
geological processes