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Uploaded on:
11/03/2009 05:35:13
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110.26 KB
1000 x 775 pixels
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P number: P521521
Caption: Mineral specimen of onyx amygdale. Dunure Railway, Brown Carrick Hills, Ayrshire.
Description: The image shows part of an onyx amygdale formed of parallel-banded chalcedony. It is unusual in that it contains an elongate fragment of dark brown 'shale' which appears to represent a sliver of the surrounding host rock which has broken away and become incorporated into the amygdale. British Geological Survey Petrology Collection sample number E 3297A. Agate and onyx are names for particular varieties of silica. Onyx band in agates form due to gravitational settling of large colloidal silica particles in a gel. On crystallizing they form chalcedonic bands. This specimen is from the Maybole Volcanic Series of the Old Red Sandstone (Devonian) rocks of the Carrick Hills in Ayrshire. The Maybole Volcanic Series is noted for its thin lavas with vesicles infilled with quartz, chalcedony and agate. The specimen was presented by John Smith, the author of the book 'Semi-precious stones of Carrick' (1910).
Date taken: 01/01/2003
Photographer: Unknown
Copyright statement: NERC
Orientation: Landscape
Size: 110.26 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/ Rocks and minerals  


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