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-Stage 1.4-

Igneous Rocks

 

Igneous Rock Cycle

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 surface

 

 

 

 

Igneous Rocks


Types of Igneous Rocks


Identifying Igneous Rocks

 

The basic types of Igneous Rocks are listed below

Types of Rocks

Textures

Composition
Felsic Intermediate Mafic Ultramafic

Intrusive (Plutonic)

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

Extrusive (Volcanic)

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

 


Petrogenesis (Creating Rocks)

 

Volcano

 


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)

Textures

     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.

 

Pegmatitic

 

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

 

Phanertitic

 

     Non-Visible Crystals:

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

 

Aphanitic

 

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

 

Porphyritic

 

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

 

Glassy

 

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

 

Vesicular

 

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

 

Pyroclastic

 

 

Compositions

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

 

Felsic

 

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

 

Intermediate

 

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

 

Mafic

 

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

Ultrmafic