HERVE CONGE, ISM / SCIENCE PHOTO LIBRARY HERVE CONGE, ISM / SCIENCE PHOTO LIBRARY
Basalt rock crystals. Polarised light micrograph of a sample of basalt, showing crystals (blue) in a matrix of finer-grained rock. The colours seen, and the physical appearance of the rock, depend on the exact mineral content of the rock and how the rock was formed. Basalt is a volcanic rock, and is formed by cooling from lava. Magnification: x30 when printed 10cm wide.
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