NRC Publications Archive Archives des publications du CNRC Angastonite, CaMgAl₂(PO₄)₂(OH)₄·7H₂O : A new phosphate mineral from Angaston, South Australia Mills, S. J.; Groat, L. A.; Wilson, S. A.; Birch, W. D.; Whitfield, P. S.; Raudsepp, M. This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur. For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous. Publisher’s version / Version de l'éditeur: https://doi.org/10.1180/minmag.2008.075.5.1011 Mineralogical Magazine, 72, 5, pp. 1011-1020, 2008-10 NRC Publications Record / Notice d'Archives des publications de CNRC: https://nrc-publications.canada.ca/eng/view/object/?id=660b91f8-9276-4e97-95b5-d0e1521cde25 https://publications-cnrc.canada.ca/fra/voir/objet/?id=660b91f8-9276-4e97-95b5-d0e1521cde25 Access and use of this website and the material on it are subject to the Terms and Conditions set forth at https://nrc-publications.canada.ca/eng/copyright READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site https://publications-cnrc.canada.ca/fra/droits LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB. Questions? Contact the NRC Publications Archive team at [email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information. Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected]. Mineralogical Magazine, October 2008, Vol. 72(5), pp. 1011–1020 Angastonite, CaMgAl2(PO4)2(OH)4·7H2O: a new phosphate mineral from Angaston, South Australia 1, 1 1 2 3 1 S. J. MILLS *, L. A. GROAT ,S.A.WILSON ,W.D.BIRCH ,P.S.WHITFIELD AND M. RAUDSEPP 1 Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 2 Geosciences, Museum Victoria, GPO Box 666, Melbourne, Victoria, 3001, Australia 3 Institute for Chemical Process and Environmental Technology, National Research Council of Canada, Montreal Road, Ottawa, ON, Canada K1A 0R6 [Received 16 June 2008; Accepted 11 December 2008] ABSTRACT Angastonite, ideally CaMgAl2(PO4)2(OH)4·7H2O, is a newly defined mineral from the Penrice marble quarry, South Australia, Australia. The mineral occurs as snow-white crusts and coatings up to about 1 mm thick associated with minyulite, perhamite, crandallite and apatite-(CaF). The streak is white, the lustre is pearly and the estimated hardness is 2 on the Mohs scale. Angastonite forms platy crystals with the forms {010} (prominent), {101}, {101¯} and {100} (rare), and also occurs as replacements of an unknown pre-existing mineral. There is one cleavage direction on {010} and no twinning has been observed. Angastonite is triclinic, P1¯, with a = 13.303(1) A˚ , b = 27.020(2) A˚ , c = 6.1070(7) A˚ a = 89.64(1)º, b = 83.44(1)º, g = 80.444(8)º, V = 2150.5(4) A˚ 3, with Z = 6. The mineral is optically biaxial (+), with refractive indices of a = 1.566(2), b = 1.572(2) and g = 1.584(2) and with 2Vmeas = 70(2)º and 2Vcalc = 71º. Orientation: X˜ a,Y˜ b,Z˜ c; with crystals showing parallel extinction and no axial 3 3 dispersion. Dmeas is 2.47 g/cm , whilstD calc is 2.332 g/cm . The strongest four powder-diffraction lines ˚ ¯ [d in A,(I/Io), hkl] are: 13.38, (100), 020; 11.05, (25), 110; 5.73, (23), 101, 230 and 111; 8.01, (21), 130. Angastonite is likely to be related to montgomeryite-group members and have a similar crystal structure, based on slabs of phosphate tetrahedra and Al octahedra. KEYWORDS: angastonite, new mineral, Penrice marble quarry, Angaston, South Australia, Australia, montgomeryite, perhamite. Introduction Angaston-Kapunda district, approximately 70 km THERE are several mineralogically significant northeast of Adelaide, have been mined inter- phosphate deposits in the Mount Lofty Ranges mittently for phosphate since the early 1900s of southeastern South Australia, Australia. Their (Jack, 1919; Johns, 1962) and have also been a hosts are low-grade phosphorite horizons within source of unusual phosphate minerals for the Cambrian marine sedimentary sequence of the collectors and researchers (Segnit and Watts, Kanmantoo Trough, which overlies the 1981; Jones, 1983). Amongsttheserare species Proterozoic Adelaide Geosyncline (Drexel and are peisleyite (Pilkington et al., 1982), alderma- Preiss, 1995). The deposits have been variably nite (Harrowfield et al., 1981), perhamite (Mills, modified by metamorphism, followed by 2003; Mills et al., 2006) and the new hydrated secondary enrichment and weathering during the calcium magnesium aluminium phosphate, angas- Tertiary. A number of small deposits in the tonite, the subject of this paper. The original samples of angastonite were collected between 1988 and 1989 by Mr Vince Peisley at the Penrice marble quarry, ~2 km north * E-mail: [email protected] of the town of Angaston (34º28’54’’S, 139º2’48’’E) DOI: 10.1180/minmag.2008.072.5.1011 (Fig. 1a,b). The mineral is named for the town, # 2008 The Mineralogical Society S. J. MILLS ET AL. FIG.1.(a) Location map of the Penrice marble quarry in relation to South Australia and Adelaide; and (b) Map showing the Penrice area, with the outcrop extent of the Angaston Marble (pale blue). which was originally known as German Pass, but phosphate mineralization at the Penrice quarry was later named after George Fife Angas occurred in a gossanous zone above recrystallized (1789À1879), businessman and Member of limestone (Figs 1b, 2). Early descriptions by Jack Parliament of South Australia, who settled in the (1919) of quarrying in the region extending a few area in the 1850s. The mineral data and name kilometres north from Angaston (sections 334 and (IMA 2008À008) have been approved by the 1734, Hundred of Moorooroo) referred to IMA Commission on New Minerals, extensive marble deposits, with phosphatic rock Nomenclature and Classification prior to publica- occurring in overlying dark soil and clay tion. The type specimens are preserved in the associated with outcrops of ‘limonite’ and collection of Museum Victoria, registered as containing residual fragments of marble. Bands M45575 and M50494. of decomposed mica schistwere also noted.Now named the Angaston Marble (or Kapunda Marble), the recrystallized limestone underlying Occurrence and geology the region is a lensoid reef deposit some 300 m The larger and more prolific phosphate deposits in thick, within the Early Cambrian Normanville the district are associated with reworked phos- Group. Having been metamorphosed, recrystal- phorite (e.g. the Moculta or Klemm’s quarry; lized and folded, the marble now occurs in the Tom’s quarry at Kapunda). The more restricted near-vertical eastern limb of a south-plunging 1012 ANGASTONITE, A NEW PHOSPHATE MINERAL FIG. 2. Aerial photograph of the Penrice marble quarry in the late 1980s, showing the dark-brown phosphate zone (arrowed) above the marble. Photograph from Vince Peisley. anticlinal structure. At the Penrice quarry, a Appearance and physical properties 5À20 m thick contact zone of calc-silicates Angastonite occurs as snow-white crusts and separates the marble from a weathered biotite- coatings up to about 1 mm thick on a matrix of rich schist of undetermined thickness and age dark-brown iron oxyhydroxides, which have (A. Steinert, personal communication). The heavily impregnated soft yellowish micaceous geological features of phosphorite found at the clay (Fig. 3). Scanning electron microscope Penrice quarry have notbeen well documented, and the original phosphate mineralization in the weathering zone has been removed through the enlargement of the quarry, now the largest source of lime in South Australia. Production is ~1.1 Mt/y, most of which is used for soda ash production, with the balance for cement, construc- tion materials, whiting and agricultural lime. Surviving specimens from the gossanous zone consistof vuggy limoniticclay enclosing small relict biotite flakes. Irregular cavities within this material are coated with compact dark-brown goethite, in turn encrusted by white phosphate mineralization. The mineralogy is quite limited, with minyulite being the most common mineral observed, in places encrusted with perhamite, crandallite or angastonite. Apatite-(CaF) FIG. 3. Portion of the type specimen (M50494) showing (formerly fluorapatite; Burke, 2008) has also intergrown crystals of angastonite on dark-brown iron been recorded from the quarry (Mills, 2003). oxyhydroxides. The field of view is 3 mm across. 1013 S. J. MILLS ET AL. FIG. 4. Scanning-electron-microscope image of angastonite crystals on the type specimen (M50494). Crystals are up to 100 mm across on edge. (SEM) images show several habits for angasto- pearly and the estimated hardness is 2 (on crystal nite, including platy crystals showing the forms aggregates) on the Mohs scale. Individual crystal {010} (prominent), {101}, {101¯} and {100} fragments are transparent, whilst intergrown (rare) (Fig. 4) and aggregates of contorted aggregates appear translucent. There is one tabular platelets (Fig. 5) which appear to have cleavage direction on {010} and no macroscopic replaced crystals of a pre-existing phosphate or microscopic twinning has been observed. The mineral. Individual angastonite crystals are up to measured density is 2.47 g/cm3, determined by about100 mm on edge butonly about1 À2 mm suspension of angastonite in methylene iodide thick (Fig.