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A calcian ralstonite-like mineral from the Cleveland Mine, Tasmania, Australia

Published online by Cambridge University Press:  05 July 2018

W. D. Birch  and
A. Pring
W. D. Birch
Affiliation:
Department of Mineralogy and Petrology, Museum of Victoria, 285 Russell Street, Melbourne, Victoria, 3000
A. Pring
Affiliation:
Department of Mineralogy, South Australian Museum, North Terrace, Adelaide, South Australia, 5000
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Abstract

A calcium-rich ralstonite, forming colourless octahedral crystals up to 2 mm across, occurs in a F-rich assemblage at the Cleveland Mine, northwestern Tasmania. Other minerals present include well-crystallized morinite, gearksutite, vivianite, siderite, K-rich feldspar (adularia), fluorite and quartz. The F-rich assemblage probably formed during greisenization when Na and F-rich magmatic brines reacted with enclosing carbonate host rocks to produce hydrothermal Na-Ca-Mg-bearing solutions. Chemical analysis of the ralstonite-like mineral gave a formula (Na1.47Ca0.52)(Mg1.49Al0.55P0.04)F6 [(OH)0.43O0.36F0.21)].

This differs from the ‘pyrochlore’ formula, due to the substitution of Ca + (OH,O,F) for H2O, in addition to the coupled substitution of Na + Mg for Al in ‘normal’ ralstonites. The Cleveland Mine ralstonite has the highest recorded Ca, Na and Mg contents. While the mineral is likely to be a new species on chemical grounds, single crystal X-ray photographs indicate the structure is disordered, possibly composed of small compositional domains.

Keywords

ralstoniteCleveland MineTasmaniaAustralia
Type
Mineralogy and Petrology
Information
Mineralogical Magazine , Volume 54 , Issue 377 , December 1990 , pp. 599 - 602
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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