PORPHYRY DYKES IN GRANITE - Cornwall
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Hingston Down Quarry, Gunnislake, Cornwall
A good specimen of granite with conspicuous dykes.
A dyke is a sheet of formerly molten rock that was forced up through a vertical crack in a pre-existing rock. The dykes cutting through the fine grained Hingston Down granite consist of dark (boron-rich) igneous rock containing crystals of feldspar. Rocks with large crystals in a fine-grained groundmass are described as having a ‘porphyritic’ texture.
Click on a picture for a larger image
Size: approx. 12 x 8 x 8 centimetres
Weight: 796 grams
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