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Lamproite |
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Lamproite |
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Lamproite is an igneous rock
deep from within the earth's magma. |
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This rock is from the Kimberley in Western Australia |
This is a fine grained rock like basalt but it does not represent a lava flow. Imagine instead a very violent, explosive eruption from a narrow volcanic vent. Rock fragments, volcanic ash (rapidly-solidified lava) and glowing, molten material become mixed up together. Some will be thrown on to the surface around the vent but some will remain in the vent and go solid there. Rocks formed of volcanic ash (rapidly-solidified lava) and fragments are usually called 'tuffs'. You can see that this rock is made up of a mixture of fragments, pellets and crystals. In this case the molten material came from great depth where the pressures and temperatures are right for diamonds to form. This zone is below the Earth's crust , in the upper mantle, over 150 km below the surface of the Earth. As molten rock rushed to the surface, it swept up diamonds and other fragments typical of the upper mantle like the minerals of olivine and garnet. |
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Associated with the tuffs in the pipe is solidified lamproite lava which can also contain diamonds.
Lamproite tuff Photographed at the Geological Museum in Perth See our section on Gems and how they are formed for more information about diamonds in Western Australia. We would like to thank the "Geological Museum of the University of Western Australia" for the information supplied. |
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and graphical Copyright © Wildlife Education Services 2003. |
