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Uploaded on:
11/03/2009 05:44:16
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P number: P521546
Caption: Mineral specimen of prehnite. Boyleston Quarry 0.5 mile north-west of Barrhead Station, Renfrew, Lanarkshire.
Description: The specimen consists of pale green or whitish prehnite, forming a surface coating inside a cavity in a basaltic rock. British Geological Survey Petrology Mineral Collection sample number 406?. Such cavities are formed by gas bubbles as the volcanic rock solidifies. Later, hydrothermal fluids percolating through the rock precipitate the mineral onto the cavity walls. Such open, partially mineralized cavities are termed 'drusy cavities'. Prehnite is a hydrous calcium aluminium silicate belonging to the orthorhombic crystal system. This specimen of prehnite is from Boylston Quarry in Renfrewshire. The locality is mentioned in Heddle's Mineralogy of Scotland. It occurs in large quantities in misshapen druses in the harder parts of porphyritic basic lavas. The prehnite at this locality is usually pale-green in colour with isolated hemispheres of a fine yellow colour. Heddle reports rare druses containing light green and milky-white prehnite.
Date taken: 01/01/2003
Photographer: Unknown
Copyright statement: NERC
Orientation: Landscape
Size: 175.68 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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