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-Stage 1.4-


Igneous Rocks


Definition - Igneous rocks form from the solidification of molten rock (AKA lava or magma)


Lava - molten rock above the ground surface

Magma - molten rock below the ground surfaceIgneous Rock Cycle



Extra Credit



Igneous Rocks Page Layout






Igneous Rocks and Volcano Resources


Since a large percentage of Igneous Rocks come from volcanoes, one of the most widely known of geologic hazards, I figured I would add some Volcano Resources to the Igneous Rocks page.


Igneous Rocks               Global Volcanism Program



Volcano Hazards Program


Eruptions - Volcanism Blog




Types of Igneous Rocks

Identifying Igneous Rocks


The basic types of Igneous Rocks are listed below

Types of Rocks


Felsic Intermediate Mafic Ultramafic

Intrusive (Plutonic)

Pegmatitic Granitic Pegmatite Dioritic Pegmatite Gabbroic Pegmatite  
Phaneritic Granite Diorite Gabbro Peridotite

Extrusive (Volcanic)

Aphanitic Rhyolite Andesite Basalt  
Glassy Obsidian Basaltic Glass  
Vesicular Pumice Scoria  
Pyroclastic Volcanic Tuff  


Petrogenesis (Creating Rocks)




Bowen's Reaction Series


Bowen's Reaction Series


Understanding Bowen's Reaction Series


Definitions Used for Identification

(Click on the images for a larger image)



     Visible Crystals:


Pegmatitic - This is when the crystals in the rock are larger than 1 cm across. This is the most common type of rock where gem stones are found due to the large crystal size.




Phaneritic - This is when crystals are between 1 mm and 1 cm




     Non-Visible Crystals:


Aphanitic - This is when there are no visible crystals in the rock




Porphyritic - This is when the background are not visible but there are large crystals "floating" in the mass




Glassy - This is when there are no visible crystals and the surface is reflective (i.e. like glass)




Vesicular - This is when the rock contains lots of air holes, causing the rock to be lighter then usual




Pyroclastic - This is when the rock forms from angular pieces of other rocks in a aphanitic matrix (similar to porpharitic but larger/angular crystals/ rock chunks)






Felsic - "light" rocks, contain light colored minerals (Also low temp minerals See Bowen's Below) (quartz, Potassium feldspar, micas)




Intermediate - A mixture of felsic and mafic, "salt and pepper" "light and dark" (Potassium feldspar, Sodium Plagioclase, Biotite, Amphibole)




Mafic - "dark" rocks, contain dark colored minerals (Also high temp minerals See Bowen's Below) (Pyroxene, Amphibole, Calcium Plagioclase)




Utramafic - "green" rocks, contain green colored minerals (The highest temp on Bowen's) (Olivene)