Rocks / Microdiorite. Pembrokeshire.

  Microdiorite is a medium grained intrusive igneous rock.This specimen was collected from a coastal super quarry at Pen Clegyr to the west of Porthgain in Pembrokeshire. The feldspars in the microdiorite were altered by hydrothermal activity to clays, making it a very useful material in the production of Porthgain bricks. The coastal location was advantageous in transporting the bricks by sea.

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