| P number: | P521480 |
|---|---|
| Caption: | Rock specimen of contact of granite and hornfels. At Drunjohn, Kirkgunzeon, 4.5 miles north-north-east of Dalbeattie, Kirkcudbrightshire. |
| Description: | The sample is a contact rock between pale coarse-grained crystalline granite and fine-grained altered sedimentary rock or hornfels. The granite contains common grains of glassy quartz and pinkish-grey feldspar with black biotite mica. The contact rock is very fine-grained and rather flinty due to the alteration, but retains a trace of sedimentary bedding with alternating black and dark greenish bands. British Geological Survey Petrology Collection sample number EMC 3764. A contact rock is one which has undergone thermal alteration or 'contact metamorphism' by the close proximity of a hot molten igneous rock. The altered rock is commonly described as a 'hornfels' which is a fine-grained rock composed of an interlocking mosaic of equigranular minerals without preferred orientation. Contact rocks containing distinct large metamorphic mineral growth are described as porphyroblastic. The specimen is part of the Criffel Granite, a large plutonic intrusion measuring 27x11 km., and is one of the many granites associated with the Caledonian Orogeny. It has been dated using radiometric techniques at 397 Ma. The Criffel Granite is composed of three granodiorites and associated quartz-diorite rocks intruded into Silurian and Ordovician sedimentary rocks, the strike of which has been deflected by the emplacement. Gravity measurements indicate that the granite is of batholithic shape and has a depth exceeding 11 km. |
| Date taken: | Wed Jan 01 00:00:00 GMT 2003 |
| Photographer: | Unknown |
| Copyright statement: | NERC |
| Orientation: | Landscape |
| Size: | 224.51 KB; 1000 x 775 pixels; 85 x 66 mm (print at 300 DPI); 265 x 205 mm (screen at 96 DPI); |
| Average Rating: | Not yet rated |
| Categories: | Unsorted Images |
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