P521522

Uploaded on:
11/03/2009 05:35:35
Type:
Digital Asset
File Size:
125.59 KB
Dimensions:
1000 x 775 pixels
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P number: P521522
Caption: Mineral specimen of agate amygdale. Brown Carrick Hills, Ayrshire.
Description: The specimen is an agate amygdale, consisting of concentrically-banded chalcedony, with a pale blue-white outer fringe and pinkish interior. British Geological Survey Petrology Collection sample number E 3303A. The agate has formed from hydrothermal fluids which have percolated through the rock and infilled open cavities (or vesicles). Once filled, these mineralized cavities are known as amygdales. Agates are found in a number of places in Scotland, however the Midland Valley is one of the better places to find them. During the Devonian (Old Red Sandstone) there was widespread vulcanicity, and andesite and basalt lavas are found with agates forming cavity fillings. The cavities are formed when a molten lava containing gases cools down, the gases try to escape, however, sometimes the gases become trapped near the top of the lava flow and form bubbles producing a cold lava full of small holes called vesicles. Silica-bearing solutions penetrate and fill the vesicles from which the agates form. 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: 125.59 KB; 1000 x 775 pixels; 85 x 66 mm (print at 300 DPI); 265 x 205 mm (screen at 96 DPI);
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Categories: Best of BGS Images/ Rocks and minerals  

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