GRANITE PORPHYRY (ELVAN) - Cornwall
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GRANITE PORPHYRY 'ELVAN' DYKE
Old Gunnislake Mine, Calstock, Cornwall
A dyke is a sheet of formerly molten rock that was forced up through a vertical crack in a pre-existing rock.
This quartz-feldspar porphyry is also known as 'elvan' - a Cornish mining term. It was intruded as a magma into the strata ('killas') surrounding the granite. The large crystals of feldspar can be clearly seen.
It was collected in 1969. It has cut faces on all sides.
Click on a picture for a larger image
Size: 10 x 7 x 6.5 centimetres
Weight: 957 grams
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