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Rocks. ESCI 1214 Fall 2006 NOC-Stillwater. What are rocks?. Rocks are aggregates of minerals They can form from several different processes There are three (3) main types: Igneous Sedimentary Metamorphic. Igneous Rocks.

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ESCI 1214

Fall 2006


what are rocks
What are rocks?
  • Rocks are aggregates of minerals
  • They can form from several different processes
  • There are three (3) main types:
    • Igneous
    • Sedimentary
    • Metamorphic
igneous rocks
Igneous Rocks
  • Igneous rocks form from the crystallization of magma (molten rock).
  • Igneous comes from the term “ignis” meaning fire.
  • This crystallization forms as the magma cools. The size of the crystals depends on the speed at which the magma cools.
  • Examples include granite, rhyolite, basalt, gabbro and diorite.
igneous rocks cont
Igneous Rocks cont . . .
  • Igneous rocks are classified by there texture and composition.
  • The texture is determined by the rate of cooling. The slower the cooling, the larger the crystals (coarse grained). The faster the cooling, the smaller the crystals (fine grained). If the magma starts cooling slowly, then cools quickly, it is said to have porphyritic texture (some coarse grains mixed in with fine grain texture).
where igneous rocks form and how it impacts crystal size
Where igneous rocks form and how it impacts crystal size


(fine-grained, cools quickly at the surface)


(coarse-grained, cools slowly at depth)

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field classification
Field Classification


bowen s reaction series
Bowen’s Reaction Series

The Bowen’s Reaction Series helps identify the minerals one would expect in a certain rock type. In addition, it helps predict the stability of each rock type and mineral at the earth’s surface




Gabbro Basalt


Diorite Andesite



Granite Rhyolite

sedimentary rocks
Sedimentary Rocks
  • Detrital Sedimentary rocks form as the result of lithification (the compaction and cementation) of sediments. The sediments come from the weathering of pre-existing rock, followed by transportation and deposition. Over time, the sediments are buried and then compacted and cemented into rock.
sedimentary rocks cont
Sedimentary Rocks cont . . .
  • Sedimentary rocks are classified by their texture as well. The size and shape of the grains tell the story of the sediments.
  • If the grains are large, they have not been broken up, or transported, as far.
  • If grains are rounded, they have been transported a substantial distance.
non detrital sedimentary rocks
Non-Detrital Sedimentary Rocks
  • Chemical/Bio-chemical Sedimentary Rocks
    • Includes carbonates such as limestone
    • Includes evaporites such as Rock Salt (halite) and Rock Gypsum
  • These sedimentary rocks form from the precipitation (or evaporation) of the chemicals from solution or from the secretion of minerals from animal life.
sedimentary rock formation
Sedimentary rock formation

Once rocks are exposed to the surface, the weathering process begins. Weathering breaks rocks down followed by transportation, deposition and lithification forming sedimentary rocks.

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metamorphic rocks
Metamorphic Rocks
  • Metamorphic rocks form from the alteration of pre-existing rock.
  • The altercation results from heat, pressure and chemically active fluids.
  • Metamorphic rocks are classified by the degree of metamorphism and the mineral content.
metamorphic rocks cont
Metamorphic Rocks cont . . .
  • There are two (2) types of metamorphism. They are contact and regional.
  • Contact metamorphism is a localized metamorphism where a rock is essentially baked.
  • Regional metamorphism occurs over a much larger area and is the result of large scale deformation (such as in a mountain building episode).
metamorphic rock formation
Metamorphic Rock Formation

Example of metamorphic rock formation. We will be more concerned with the regional and contact metamorphism types.

Regional metamorphism involves extreme pressure with some heat over a large area

Contact metamorphism involves extreme heat over a localized area

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the rock cycle
The Rock Cycle
  • The rock cycle explains the system by which rocks are formed, weathered, altered, etc. over millions and millions of years.
the rock cycle20
The Rock Cycle

The Rock Cycle is a continuous process that changes old rock, creates new rock and recycles rock