GEORGE BERNARD / SCIENCE PHOTO LIBRARY GEORGE BERNARD / SCIENCE PHOTO LIBRARY
Red granite. Cut surface of red granite, showing the rock's coarsely crystalline structure. The coloured fragments are crystals of the various minerals that make granite - mostly quartz, mica & feldspar. The red colour is due to impurities in the feldspar. An igneous rock, granite is formed from molten "magma", which rises from deep in the Earth and then solidifies. Large crystals grow in granite because the magma cools down slowly under- ground. The very big crystals in this sample are phenocrysts. These are the first to form as the magma cools, and consist of minerals with the highest crystallization temperature - in this case feldspar. Magnification x0.25 at 35mm size.
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