| P number: | P521241 |
|---|---|
| Caption: | Rock specimen of chert. Shore, west of Balnakiel, Durness, Sutherland, Scotland. |
| Description: | The rock is strongly banded with thin alternating parallel layers of varying pale whitish colours, greys and black. Each layer represents a band of silica of slightly different composition, the varying colours probably resulting from the presence of relatively minor impurities. British Geological Survey Petrology Collection sample number EMC323. Chert is a very fine-grained rock consisting entirely of silica, often termed 'cryptocrystalline', with a typically vitreous or dull lustre. It has variable colour, often dependant on very small impurities. It is very hard and dense, with a splintery fracture, and was used by ancient peoples as a cutting tool. The chert is from the Cambrian-Ordovician Durness Group of limestones, dolomitic limestones and dolostones (fine-grained carbonate rocks grading from pure limestone to dolomite). Some horizons have chert bands or chert nodules. The Durness Group was laid down on gently subsiding warm shelf sea. |
| Date taken: | Sun Dec 01 00:00:00 GMT 2002 |
| Photographer: | McTaggart, F.I. |
| Associate: | T.S. Bain |
| Copyright statement: | NERC |
| Additional information: | EMC323 |
| Orientation: | Landscape |
| Size: | 204.48 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: | Best of BGS Images/ Geological structures |
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