Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 250–256 Contents lists available at SciVerse ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa A vibrational spectroscopic study of the phosphate mineral 2+ 2+ zanazziite – Ca2(MgFe )(MgFe Al)4Be4(PO4)6Á6(H2O) ⇑ Ray L. Frost a, , Yunfei Xi a, Ricardo Scholz b, Fernanda M. Belotti c, Luiz Alberto Dias Menezes Filho d a School of Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty, Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia b Geology Department, School of Mines, Federal University of Ouro Preto, Campus Morro do Cruzeiro, Ouro Preto, MG 35400-00, Brazil c Federal University of Itajubá, Campus Itabira, Itabira, MG 35903-087, Brazil d Geology Department, Institute of Geosciences, Federal University of Minas Gerais, Belo Horizonte, MG 31270-901, Brazil highlights graphical abstract " We have analyzed the phosphate mineral zanazziite and determined its formula. " The mineral was studied by electron microprobe, Raman and infrared spectroscopy. " Multiple bands in the bending region supports the concept of a reduction in symmetry of phosphate anion. article info abstract Article history: Zanazziite is the magnesium member of a complex beryllium calcium phosphate mineral group named Received 13 August 2012 roscherite. The studied samples were collected from the Ponte do Piauí mine, located in Itinga, Minas Ger- Accepted 5 November 2012 ais. The mineral was studied by electron microprobe, Raman and infrared spectroscopy. The chemical for- Available online 5 December 2012 mula can be expressed as Ca2.00(Mg3.15,Fe0.78,Mn0.16,Zn0.01,Al0.26,Ca0.14)Be4.00(PO4)6.09(OH)4.00Á5.69(H2O) and shows an intermediate member of the zanazziite–greinfeinstenite series, with predominance of zan- Keywords: azziite member. Raman spectroscopy The molecular structure of the mineral zanazziite has been determined using a combination of Raman Infrared spectroscopy and infrared spectroscopy. A very intense Raman band at 970 cmÀ1 is assigned to the phosphate symmet- Zanazziite À1 Roscherite group ric stretching mode whilst the Raman bands at 1007, 1047, 1064 and 1096 cm are attributed to the Greinfeinstenite phosphate antisymmetric stretching mode. The infrared spectrum is broad and the antisymmetric À1 Phosphate stretching bands are prominent. Raman bands at 559, 568, 589 cm are assigned to the m4 out of plane bending modes of the PO4 and HPO4 units. The observation of multiple bands supports the concept that the symmetry of the phosphate unit in the zanazziite structure is reduced in symmetry. Raman bands at 3437 and 3447 cmÀ1 are attributed to the OH stretching vibrations; Raman bands at 3098 and 3256 are attributed to water stretching vibrations. The width and complexity of the infrared spectral profile in con- trast to the well resolved Raman spectra, proves that the pegmatitic phosphates are better studied with Raman spectroscopy. Ó 2012 Elsevier B.V. All rights reserved. Introduction Zanazziite is a calcium and magnesium beryllium hydrated ⇑ Corresponding author. Tel.: +61 7 3138 2407; fax: +61 7 3138 1804. phosphate mineral from the rosherite group. Zanazziite arises as E-mail address: [email protected] (R.L. Frost). barrel-shaped crystals and can reach up to 4 mm. It grows along 1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2012.11.017 R.L. Frost et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 250–256 251 side quartz or in association with others secondary phosphate min- The value for the m2 symmetric bending vibration of PO4 units as erals, including eosphorite–childrenite, montebrasite, beryllonite, determined by infrared spectroscopy was given as 438 cmÀ1 (aug- fluorapatite and brazilianite. It was first found in miarolitic cavities elite), 452 cmÀ1 (wavellite), 440 and 415 cmÀ1 (rockbridgeite), in the granitic pegmatite named Lavra da Ilha, near Taquaral, 455, 435 and 415 cmÀ1 (dufrenite) and 470 and 450 cmÀ1 (bera- municipality of Itinga, in northeastern Minas Gerais, Brazil. unite). The observation of multiple bending modes provides an Zanazziite is named after Dr. Pier F. Zanazzi. Zanazziite has an ideal indication of symmetry reduction of the PO4 units. This symmetry chemical formula of Ca2Mg5Be4(PO4)6(OH)4Á6H2O [1]. reduction is also observed through the m3 antisymmetric stretching Zanazziite is one of the members of the roscherite group, which vibrations. Augelite shows infrared bands at 1205, 1155, 1079 and is a complex group of calcium and beryllium phosphates of general 1015 cmÀ1; wavellite at 1145, 1102, 1062 and 1025 cmÀ1; rock- À1 formula: Ca2(M1)2(M2) 4Be4(PO4)6(OH)4X2Á4H2O; where M1 and M2 bridgeite at 1145, 1060 and 1030 cm ; dufrenite at 1135, 1070 2+ 2+ 3+ À1 are octahedral sites. M1 is occupied by Mg, Mn ,Fe ,Fe , Zn, and and 1032 cm ; and beraunite at 1150, 1100, 1076 and À1 Al, however the Al dominant member is unknown. The M1 can be 1035 cm . In the infrared study of triploidite, a basic manganese also partially vacant. The M2 sites are essentially vacant, their phosphate, Farmer reports the infrared spectrum with the (m1)at À1 À1 common occupancy usually being 1/3–1/2 per formula unit. 957 cm ,(m3) at 1090, 1058, 1030 and 1010 cm ,(m2)at À1 À1 X = OH or H2O. In addition to zanazziite, others minerals in rosche- 420 cm and the m4 mode at 595, 570, 486 cm [12]. A hydroxyl rite group are namely atencioite, footemineite, greinfenstenite, stretching frequency of 3509 cmÀ1 was given. In the spectroscopic guimarãesite, roscherite and ruifrancoite [2]. Due to the complex- study of strengite, in the region below to 400 cmÀ1, Frost and We- ity of the roscherite group, Rastsvetaeva et al. (2005) general ier [17] described the metal stretching vibrations for MnO and also formula as Ca2M5Be4(PO4)6(OH)4Án(H2O), where M is occupied by the OMnO bending modes. Mn, Fe, Zn, Mg and Al and n 6. In this work, samples of a pure, monomineral zanazziite from Zanazzite belongs to the monoclinic crystal system, space group the Ponte do Piauí pegmatite, located in the municipality of Itinga, 0 0 C2/c [3–5]0. The unit cell parameters are: a = 15.876 ÅA, b = 11.860 ÅA, Minas Gerais, Brazil has been carried out. Studies include chemis- c = 6.607 ÅA, and b = 95.49°. The axial ratio of zanazziite is try via electron microprobe analysis in the WDS mode (EMP), spec- a = 1.3391, b = 1 and c = 0.5571. There is uncertainty in analyzing troscopic characterization of the structure with infrared and zanazziites distribution of cations on M1 and M2 sites. The M2 site Raman spectroscopy. in zanazziite is indistinct; it contains two Me–O bond distances, and two Me–OH bond distances. In X-ray scattering and diffraction models the data presents an approximation of the number of Geological setting, occurrence and general appearance electrons in each atomic site, giving 17.3 eÀ in the M2 site and 64.8 eÀ in the M1 site. The crystals in zanazziite are prismatic to The studied samples were collected from the Ponte do Piauí bladed, usually rough, barrel-shaped, with indices {100}, {110} mine, located in the Piauí valley, municipality of Itinga. The region and {001}. Cleavages are on {100} good, and {010} distinct. is well-known as an important source of rare phosphates and gem- Characterization of beryllium mineral paragenesis is an impor- ological minerals. The pegmatite is located in the Araçuaí pegma- tant tool in the petrogenetic study of granitic and alkaline pegma- tite district, one of the subdivisions of the Eastern Brazilian tites [6]. Be metal is an important element in industry with Pegmatite province (EBP) [18]. The Araçuaí pegmatite district cov- different applications in metallurgy, especially in the production ers an area of about 10,000 km2, in the northern region of Minas of copper, aluminum and magnesium alloys. Due to its stiffness, Gerais, in the Jequitinhonha River basin, about 560 km north of light weight and dimensional stability over a wide temperature Belo Horizonte. range beryllium has also importance for the defense and aerospace The Ponte do Piauí is mined for gemstones and samples for the industry. Beryllium is also a hazardous element and is responsible collectors market. The pegmatite is heterogeneous with well- to development of chronic beryllium disease (CBD) [7,8], arousing developed mineralogical and textural zoning. The pegmatite is interest in the environmental sciences. hosted by cordierite–biotite-quartz schists with minor intercala- Be phosphates are relatively rare in nature and are related to tions of calcsilicate rocks of the Salinas Formation. Tourmaliniza- the hydrothermal and supergene process in granitic pegmatites tion is observed in the contact between the pegmatite and the [9]. A number of 26 phosphate minerals are known in nature and host rock. Hydrothermal and metasomatic fluids were responsible approved by the International Mineralogical Association. Cˇerny´ for the development of miarolitic cavities. Primary phosphates [10] and Cˇerná et al. [11] described beryllium phosphates as were not observed. secondary product of latte alteration of beryl. In recent years, spec- The primary mineral association is represented by quartz, troscopic studies concerning phosphate minerals are increasing, muscovite, microcline, schorl and almandine–spessartine. The sec- especially due to their industrial and technological importance; ondary association is mainly composed by albite, Li bearing micas, however, only near-infrared vibrational spectroscopic data are cassiterite, elbaite and hydrothermal rose quartz. In the Ponte do available on zanazziite [12]. Piauí pegmatite, secondary phosphates, namely eosphorite, fluor- Farmer [13] divided the vibrational spectra of phosphates apatite, zanazziite, occur in miarolitic cavities in association with according to the presence, or absence of water and hydroxyl units albite, quartz and muscovite.