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Igneous Rock ClassificationIgneous Rock Classification
Dr. David Steer
Rock cycleRock cycle
Analysis TimeAnalysis Time
Given:Bag rocks
Group these rocks in some manner
Grouping itemsGrouping items
Group these objects in some logical way.
Color (Proxy for silica content)
Size (Proxy for grain size)
Grouping itemsGrouping items
Group these objects in some logical way.
Analysis timeAnalysis time
Given:Bag rocks
Group these rocks in some manner
Rock CycleRock Cycle
Igneous RocksIgneous Rocks Volcanic (extrusive) igneous rocks
Cool fast, small crystalsform when molten rock (magma) in the earth’s interior rises to the surface through pipes or fractures in the crust.
Igneous RocksIgneous RocksPlutonic (intrusive) igneous rocks
Cool slow, large crystals
form when magma cools within the earth. Igneous rocks that cool below the earth's surface are termed plutonic (or intrusive) igneous rocks.
Classification of Igneous rocksClassification of Igneous rocks Texture size of crystals most important
Cooling rates– Surface, fast
Small crystals
– Below surface slow Larger crystals
Which formed at surface?
Both are the same chemistry
Rhyolite Granite
a) b)
Chemical CompositionChemical Composition Color
Indicative of chemistry and temperatures of formation– Dark colors
High temperatures (1000 to 1200 oC) Low silica content
– Light colors Lower temperatures High silica content
Gabbro Granite
Which is the high silica rock?
Both formed below the surface
a) b)
TextureTexture So explain this!!!!
Six common Igneous RocksSix common Igneous Rocks
Volcanic Rocks
Silica Content
Minerals Present (in order of abundance)
Plutonic Rocks
Basalt low
pyroxene, olivine, feldspar, & amphibole
Gabbro
Andesite intermediate feldspar, amphibole, pyroxene, biotite mica
Diorite
Rhyolite high feldspar, quartz, muscovite mica, & amphibole
Granite
Solidifying Temperature 500 C1000 C
Lighter C
olor
Increasing Grain Size
Draw a concept map that guides you through classifying an igneous rock.
Use these terms to: Classify Igneous Rocks
Basalt Color Cool QuickCool Slow Dark Extrusive Gabbro Granite High SilicaLarge Grain Low Silica LightPlutonic Texture RhyoliteSmall Grain
Identify the rock type associated with the diagram below. Identify the rock type associated with the diagram below.
a. andesite porphoryb. gabbroc. basaltd. obsidian
1) Plot 12) Plot 23) Plot 34) Plot 4
Question
5) Imagine that all minerals found in rocks were the same color. What information would you no longer be able to infer?
a. texture b. cooling rate
c. composition
5) Imagine that all minerals found in rocks were the same color. What information would you no longer be able to infer?
a. texture b. cooling rate
c. composition
Analysis TimeAnalysis Time
Given:Bag rocks
Identify the rocks