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Igneous processes
Igneous rocks

Igneous rocks are rocks that form when magma cools and solidifies.
When the magma cools mineral crystals begin to grow
The texture of the rock can be:
Coarse - 7 - 2mm
Medium - 2 - 0.5mm
Fine - <0.5mm
Silicic Intermediate Basic
Fine grained Ryolite…

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Lava viscosity

Viscosity is how thick a liquid is.
A lava with a high viscosity is thick and will flow slowly and a lava with a low viscosity is runny
and will flow slowly.

Factors that change the viscosity are:
Water content
Composition (silica level)
Gas content
Temperature

Water content…

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Sills and Dykes

A sill occurs when magma intrudes between layers of sedimentary rocks. Sill are always parallel
to the rock beds.
A dyke is formed when magma has intruded into a fracture or fissure through the original
country rock. Dykes tend to be vertical and don't follow the rock…

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Volcanic textures

The texture is the size, shape and the arrangement of the crystals.

Columnar jointing
Columnar jointing is where the lava cools and contracts quickly forming hexagonal joints. The joints
are usually perpendicular to the lava flow.





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Vesicular texture
Vesicular texture are rocks that contain small vesicles (gas bubbles)
The vesicles are formed by the expansion of gas bubbles
The two rocks that have vesicular texture are pumice and scoria.






Amygdaloidal texture
Amygdaloidal rocks have lots of different minerals in them.
They are formed from the vesicles…

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