Sugilite in Manganese Silicate Rocks from the Hoskins Mine and Woods Mine, New South Wales, Australia

Y. Kawachi, P. M. Ashley, D. Vince and M. Goodwin
Geology Department, University of Otago, P.O.Box 56, Dunedin, New Zealand
Department of Geology and Geophysics, University of New England, Armidale, NSW 2351, Australia
1A Ramsay Street, Essendon, Victoria 3040, Australia
P.O.Box 314, Lightning Ridge, NSW 2834, Australia

Abstract: Sugilite relatively rich in manganese has been found at two new localities, the Hoskins and Woods mines in New South Wales, Australia. The occurrences are in manganese-rich silicate rocks of middle to upper greenschist facies (Hoskins mine) and hornblende hornfels facies (Woods mine). Coexisting minerals are members of the namansilite-aegirine and pectolite-serandite series, Mn-rich alkali amphiboles, alkali feldspar, braunite, rhodonite, tephroite, albite, microcline, norrishite, witherite, manganoan calcite, quartz, and several unidentified minerals. Woods mine sugilite is colour-zoned with pale mauve cores and colourless rims, whereas Hoskins mine sugilite is only weakly colour-zoned and pink to mauve. Within single samples, the chemical compositions of sugilite from both localities show wide ranges in Al contents and less variable ranges of Fe and Mn, similar to trends in sugilite from other localities. The refractive indices and cell dimensions tend to show systematic increases progressing from Al-rich to Fe-Mn-rich. The formation of the sugilite is controlled by the high alkali (especially Li) and manganese contents of the country rock, reflected in the occurrences of coexisting high alkali- and manganese-bearing minerals, and by high fo2 conditions.

Keywords: sugilite • manganese silicate rocks • milarite group • New South Wales • Australia

Mineralogical Magazine; December 1994 v. 58; no. 393; p. 671-677; DOI: 10.1180/minmag.1994.058.393.18
© 1994, The Mineralogical Society
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