MICHAEL MARTEN / SCIENCE PHOTO LIBRARY MICHAEL MARTEN / SCIENCE PHOTO LIBRARY
Slate quarry. Excavator moving rocks in a slate quarry. Slate, a metamorphic rock, is formed when a fine-grained sedimentary rock, such as mudstone, is subjected to high temperatures and pressures within the Earth's crust. This changes its crystal structure, and it forms a grey rock that can be split into thin, flat sheets. This property makes it a useful material for the construction industry for use as roof or wall coverings. Photographed near Machynnleth, Wales.
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