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Uploaded on:
11/03/2009 05:37:37
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P number: P521528
Caption: Mineral specimen of prehnite. Castle Hill, 3.2 km west-south-west of Kilbirnie, Ayrshire.
Description: The specimen shows the mineral prehnite forming a globular or botryoidal crust. It has an orange colour which may be caused by the presence of a secondary coating of iron oxide on its surface. British Geological Survey Petrology Collection sample number E 3317A. The mineral prehnite is silicate of calcium and aluminium. This specimen is from a vesicle or cavity in a Dalmeny-type basalt plug or volcanic neck, probably of Carboniferous age. The specimen was presented by John Smith, the author of the book 'Semi-precious stones of Carrick' (1910). Prehnite is commonly found as green or greenish-white reniform, stalactititc or mammillary aggregates. It has a hardness of 6-6.5 on Moh's scale of hardness and a perfect basal cleavage. It is translucent with a vitreous lustre.
Date taken: 01/01/2003
Photographer: Unknown
Copyright statement: NERC
Orientation: Landscape
Size: 170.58 KB; 1000 x 723 pixels; 85 x 61 mm (print at 300 DPI); 265 x 191 mm (screen at 96 DPI);
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Categories: Best of BGS Images/ Rocks and minerals  


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