Download - Igneous Rocks
Igneous RocksAre grouped by mineral composition and texture
1. Texture
Size and arrangement of mineral crystals
igneous crystals often interlocking
A. Intrusive Texture
Intrusive: formed underground from magma that cooled SLOWLY
large, easily seen crystals
Intrusive-coarse-plutonic
Igneous rocks w/ large crystals are known as: Intrusive= plutonic= coarse-grained
–ex: granite
Granite
Intrusive-Plutonic-Coarse GrainedGranite
B. Extrusive Texture
Extrusive: formed above ground from lava that cooled QUICKLY
small crystals, often hard to see
Igneous rocks w/ small crystals are known as:
extrusive= volcanic= fine-grained
–ex: basalt,
–rhyolite
Rhyolite:Extrusive
Fine GrainedVolcanic
Basalt:
ExtrusiveFine GrainedVolcanic
2. Composition
Is the mineral content often shown as color of rock
A. Felsic
Felsic rocks
–are light colored
–have hi silica content
–most intrusive rox are felsic
felsic
Granite
Rhyolite
B. Mafic
Mafic rocks are:–dark colored–low in silica–most extrusive rocks are mafic
•ex: basalt
Basalt
Some igneous rocks are hard to classify: Obsidian: glassy
Porphyritic: full of holes
porphyritic
pumice: full of holes; floats
scoria: full of holes; doesn’t float
Floating Pumice
Scoria
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