Schist, Scotland

The rocks in the foreground are mica schists, which also form much of the Scottish Highlands in the background.

The original rocks were laid down as sediments on an ancient sea floor over 500 million years ago. They were later caught up in the continental collision that formed the Caledonian mountains about 100 million years later. During that time, the sedimentary rocks were squashed and deformed into folds, and changed by heat and pressure to become hard, crystalline metamorphic rocks. The shiny surfaces that these schists often show are due to the presence of the flaky mineral, mica, formed during the metamorphism.