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Igneous Rocks


Formed in molten lava or magma. As it cools crystals begin to grow in the liquid. All the crystals
are touching. If not this would make it a sedimentary. If the magma cools slowing then the crystals
will be large as they have plenty of time to grow.…

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Identify other aspects of texture:
· Porphyritic: Large phenocrysts in a finer groundmass. In fine grained rocks this may result
from two stages of cooling.
· Flow banding: In finegrained lavas, light and dark bands sometimes contorted by plastic
flow. Typical of viscous lavas.
· Flow alignment: In finegrained porphyritic…

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Columnar joints

Columns can vary from 3 meters to a few centimetres in
diameter. They are typically parallel and straight but can
also be curved. The number of sides of the individuals can
vary from 3 to 8. 6 sides are the most common.




Liquid contracts around central cooling nucleus…

Page 4

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Dyke ­ Disconcordant

Moves along a fault. Lava flow is not
concordonot with beddind planes.
Baked margins either side.

Baked margins on either side

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