False-colour scanning electron micrograph (SEM) of sandstone in the process of lithification. This is an example of diagenesis, the process by which rocks are reformed from weathered fragments close to Earth's surface at low temperatures & pressures. The sandstone consists of quartz fragments of various types. The grain at centre, for instance, is covered with small, angular crystal overgrowths. This ragged texture is characteristic of partly lithified rock. Such rocks are commercially important because the partly filled voids are capable of holding oil or gas. Magnification: x25 at 35mm size. Yellow tint. Original is BW E417/019. Ref.: MICROCOSMOS, figure 7.29, page 140.
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