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Metamorphic effects on agate found near the Shap granite, Cumbria, England: as demonstrated by petrography, X-ray diffraction and spectroscopic methods

Published online by Cambridge University Press:  05 July 2018

T. Moxon ,
S. J. B. Reed  and
M. Zhang
T. Moxon*
Affiliation:
55 Common Lane, Auckley, Doncaster DN9 3HX, UK
S. J. B. Reed
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
M. Zhang
Affiliation:
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
*
E-mail: [email protected]
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Abstract

Agates from a 430 Ma host at Stockdale Beck, Cumbria, England have been characterized. The crystallite size of the Stockdale Beck agates was found to be ~60% greater than any other agates from five regions aged 400–1100 Ma. Raman spectroscopy identified moganite in all agates tested except those from Stockdale Beck. Infrared spectroscopy showed that the silanol content of the Stockdale Beck agates was near zero. The properties of agates from Stockdale Beck and the 1.84–3.48 Ga metamorphosed hosts found in Western Australia were similar but different from agates found in other hosts aged 400–1100 Ma. Cathodoluminescence demonstrates further differences between agates from hosts aged 13–1100 Ma and those from Stockdale Beck and Western Australia. Agates from the latter areas have a lower proportion of defects causing a red emission band (~660 nm) but an increased proportion of defects causing blue (~470 nm) and orange (~640 nm) emission bands. Agates found in hosts aged 13–1100 Ma are also differentiated from the Stockdale Beck and Western Australian agates in a ternary plot of the relative intensities of violet to blue to orange emission bands. Single scans producing this combination of colours are only found in the Stockdale Beck and Western Australian agates. The properties shown by the Stockdale Beck and Western Australian agates demonstrate that an agate or chalcedony infill can be used to identify post-deposition palaeoheating within a host rock.

Keywords

agatechalcedonymoganiteIRRamanXRDcathodoluminescence
Type
Research Article
Information
Mineralogical Magazine , Volume 71 , Issue 4 , August 2007 , pp. 461 - 476
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2007

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