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| Geological photographs from around the world | ||||||||
When magma cools, elements join together into the molecules which make up minerals,
depending on their freezing points (= melting point), and on the elements which are available in the magma at the
time. Different magmas are formed in different areas of the world, controlled by the activities of plate tectonics.
Magma can undergo a number of changes as it rises and evolves. Differentiation results in a sequence of
different minerals, summarised in Bowen's Reaction Series. Why a magma should melt in the first place is explained
by partial melting.
Magma in intrusions cools slowly, surrounded and insulated by crustal rocks, therefore crystallising as coarser crystals. Extrusions cool quickly to form finer crystals.
Igneous rocks form as molten magma cools, crystallises and solidifies.
The type (and name) of the rock depends on
- the composition of the magma; for example - acid/silicic or basic/mafic
- the rate at which it cools
Geopix Study Topic "Magma and Igneous Rocks"
- outlines the formation of magma
- gives a classification of igneous rocks
- explains magmatic differentiation, partial melting and other igneous processes
- describes the commoner igneous textures
- suggests how to answer exam questions on this topic
The Magma and Igneous Rocks Study Topic contains the following pages:
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To order this CD go to the Geopix Online Store