3.2 igneous rocks igneous comes from the latin word which means “fire” igneous rocks form by...
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3.2 Igneous Rocks
Igneous comes from the Latin word which means “fire”
Igneous rocks form by “crystallization” when hot molten rock solidifies.
Classifications:A. Intrusive Rocks (Plutonic Rock)
1. Rocks that form when magma hardens beneath Earth’s surface.
2. Cools slowly, forms large crystals. Example: granite
A. Extrusive Rocks (Volcanic Rock)1. Rocks that form when lava hardens at
Earth’s surface2. Cools rapidly, forms small crystals.
Example: rhyolite
3.2 Igneous Rocks
When Magma/Lava composition is mainly: quartz & feldspar (Si and O) then they are considered “Felsic.” They tend to be light in color and with a low specific gravity. (sometimes called granitic composition)
3.2 Igneous Rocks
When Magma/Lava composition is mainly olivine or pyroxine (Mg, Fe) then they are considered “Mafic.” They tend to be dark in color and with a high specific gravity. (sometimes called basaltic composition)
Formation of Igneous Rocks
1. F fire
2. C intrusive igneous (plutonic)
3. G extrusive igneous (volcanic)
4. A magma
5. D lava
6. B granite
7. E rhyolite
Composition is the same, mostly quartz, feldspar and hornblend. Texture is very different
Compare/Contrast Igneous Rocks
Granite Rhyolite
Compare Igneous, composition-quartz, feldspar, hornblend (felsic)
Igneous, made of quartz, feldspar, (felsic)
Contrast Slow cooling from magmaIntrusive/Plutonic Large crystals
Rapid cooling from lavaExtrusive/Volcanic Small crystals
Igneous Rock Classification
9. Texture and composition Texture – size, shape and
arrangement of interlocking crystals Composition – proportions of light and
dark minerals in the rock
Classification Terminology
Large Crystals/ Coarse Grained
Small Crystals/ Fine Grained
Glassy Porphyritic
Very slow coolingLarge crystals
Rapid coolingSmall interconnected crystals
Very fast coolingNo crystals
Different sized crystalsCrystals did not form at same rate
Composition TerminologyFelsic/Granitic
Mafic/ Basaltic
Other
Light colored silicate minerals
Quartz/ feldspar
Dark colored silicate minerals
Fe, Mg, plagioclase feldspar
Andesitic – Ultramafic-
andesite lava peridotite
Rock olivine &
25% dark pyroxene
Silicate and not found
plagioclase at Earth’s
Feldspar surface
Classification of Igneous Rocks10. True11. Mafic composition (basaltic)
12. a, b, c, d
13. Ultramafic
14. False
15. b