ALFRED PASIEKA / SCIENCE PHOTO LIBRARY ALFRED PASIEKA / SCIENCE PHOTO LIBRARY
Polarised light micrograph of a thin section of quartz porphyry, a type of igneous rock. Essential mineral components include quartz, alkaline feldspar and biotite. The large coloured crystals visible here are of quartz and feldspar. Large crystals, like these, embedded in a fine grained matrix are known as phenocrysts. The rock is used for building and decoration, as well as for roadbeds, ballast, grindstones and gravel. Magnification: x11 at 6x6cm size.
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