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Uploaded on:
11/03/2009 05:36:18
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P number: P521524
Caption: Mineral specimen of calcite-onyx amygdale. Dunure Railway, Brown Carrick Hills, Ayrshire, Ayrshire.
Description: The specimen is a calcite-onyx amygdale, largely formed of a single crystal of calcite. The calcite has a translucent grey appearance. The outer 'rind' of the amygdale is formed from very fine-grained white onyx. British Geological Survey Petrology Collection sample number E 3307A. Onyx is a term used to describe a variety of chalcedony that is like a banded agate, but consists of alternating bands of different colours where the bands are straight and parallel. It is well-known for use in jewellery, in particular for cameos. An unusual calcite-onyx amygdale, this specimen is from the Maybole Volcanic Series of the Old Red Sandstone (Devonian) rocks of the Carrick Hills in Ayrshire. Vesicles are very common in the lavas of the Carrick Hills, they are usually filled with quartz, chacedony or agate and less commonly calcite. Some amygdales reach a very large size, one specimen in lava on the shore 600 yards north-north-east of Dunure is six feet in diameter. 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: Portrait
Size: 170.08 KB; 874 x 1000 pixels; 74 x 85 mm (print at 300 DPI); 231 x 265 mm (screen at 96 DPI);
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Categories: Best of BGS Images/ Rocks and minerals  


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