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Gneiss, Scotland

Gneiss hand specimen
Gneiss is a metamorphic rock formed by immense heat and pressure deep within the Earth’s crust. In this photograph you can see how the rock layers have been intensely deformed at temperatures high enough to make the rock quite soft and “plastic”.

Gneiss: South Uist, Hebrides

South Uist, Hebrides. Parts of the Lewisian gneiss (named after the island of Lewis) in north-west Scotland are thought to be almost 3000 million years old; the sedimentary and igneous rocks from which they were formed must have been even older! Very similar rocks exist in east Greenland, to which Scotland was once joined, before the present-day Atlantic ocean began to form around 50 million years ago.
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