An Introduction to Geology: 3 -...
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15/10/2013 1 An Introduction to Geology: 3 Remembered Mnemonics? Thus Jogging Can Prove Notably Queasy Eating Crisps On Sundays Doubles Calorie Points
Transcript of An Introduction to Geology: 3 -...
15/10/2013
1
An Introduction to Geology: 3
Remembered Mnemonics?
Thus
Jogging
Can
Prove
Notably
Queasy
Eating
Crisps
On
Sundays
Doubles
Calorie
Points
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Igneous Rocks
Hand specimens
First impressions?
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Rock-forming minerals
Quartz
(SiO2)
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Rock-forming minerals
Feldspar
(aluminium silicates)
Orthoclase
Plagioclase (Ca-
) feldspars
Alkali (K- or
Na-) feldspars
Rock-forming minerals
Mica
(sheet silicates)
Biotite
Muscovite
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Rock-forming minerals
Calcium carbonate
– CaCO3
Aragonite
Calcite
Rock-forming minerals
Pyroxene / amphibole
(chain silicates)
Hornblende (amphi)
Augite (pyro)
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Rock-forming minerals
Olivine
(Mg-Fe silicate)
Igneous rocks
fire
magma
crystals
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Igneous
UK
Precambrian
Palaeozoic
Palaeogene
Classification
Setting
Cooling depth
Texture
Crystal size
Chemistry
Minerals
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1. Settings
Extrusive
Intrusive
Hypabyssal
Extrusive igneous rocks
Volcanic
Lava / ash
Gassy
Fine-grained
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Extrusive UK
Intrusive igneous rocks
Cooled at depth
Coarse-grained
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Intrusive UK
Hypabyssal igneous rocks
Sills / dykes
Medium-grained
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Hypabyssal UK
2. Textures >5 mm = Coarse-grained
1-5 mm = Medium-grained
<1 mm = Fine-grained
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Textures and temperature
Fine-grained = fast-cooled
Textures and temperature
Coarse-grained = slow-cooled
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Hand specimens
What texture/s are your rocks?
Volcanic temperatures
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3. Chemistry
Felsic – Intermediate – Mafic – Ultramafic
Colours and chemistry
Light coloured (felsic) minerals:
- Quartz
- Feldspar (orthoclase / plagioclase)
- Some micas (e.g. muscovite)
Dark coloured (mafic) minerals:
- Olivine
- Pyroxenes (e.g. augite)
- Amphiboles (e.g. hornblende)
- Other micas (e.g. biotite)
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Silica-based classification
More SiO2 = more viscous magma
(US Geological Survey)
Chemistry of crystals
Fractional crystallization:
1200°C
olivine 800°C
plagioclase
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Hand specimens
What chemistry is your rock?
Common igneous rocks
Granite
Intrusive
Coarse-grained
Felsic
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Common igneous rocks
Basalt
Extrusive
Fine-grained
Mafic
Common igneous rocks
Dolerite
Hypabyssal
Medium-
grained
Mafic
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Common igneous rocks
Gabbro
Intrusive
Coarse-
grained
Mafic
Common igneous rocks
Rhyolite
Extrusive
Fine-grained
Felsic
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Common igneous rocks
Andesite
Extrusive
Fine-grained
Intermediate
Igneous importance
Absolute dating
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Igneous importance
Granite
Dolerite
Igneous importance
Fertile soils
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The Volcano Chaser
Yorkshire Museum talks:
Mon. 28th Oct-Fri. 1st Nov.
Pyroclastic flow, Mt Pelee, 1902
Next week Sand, Mud & Lime:
TUESDAY
OCT. 29th
Room:
D/L/006
