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Uploaded on:
11/03/2009 05:42:06
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P number: P521540
Caption: Mineral specimen of prehnite. Castle Hill, 3.2 km west-south-west of Kilbirnie, Ayrshire.
Description: The specimen is part of an amygdaloidal cavity containing globular masses of the pale green mineral prehnite. Prehnite typically has this form, called botryoidal. The cavity, or vesicle, is an open space formed by the presence of volcanic gases within the basalt host rock. British Geological Survey Petrology Collection sample number E 3314A. Prehnite is a secondary mineral which forms in hydrothermal deposits within cavities in volcanic rocks and in the fissures of crystalline rocks. It is sometimes carved to make decorative ornaments and jewellery, such as in India. Prehnite is a hydrous calcium aluminium silicate that is commonly found as green or greenish-white reniform, stalactititc or mammilary 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. This specimen of pale green prehnite from an amygdaloidal cavity in a Dalmeny basalt plug, or volcanic neck, probably of Carboniferous age. Presented by John Smith, collected in 1922. Prehnite does not have any major uses though it is of interest to mineral collectors and scientists.
Date taken: 01/01/2003
Photographer: Unknown
Copyright statement: NERC
Orientation: Landscape
Size: 173.33 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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