Aluminium-bearing strunzite derived from jahnsite at the Hagendorf-Süd pegmatite, Germany

Abstract

Aluminium-bearing strunzite, [Mn 0.65 Fe 0.26 Zn 0.08 Mg 0.01 ] 2+ [Fe 1.50 Al 0.50 ] 3+ (PO 4 ) 2 (OH) 2 ·6H 2 O, occurs as fibrous aggregates in a crystallographically oriented association with jahnsite on altered zwieselite samples from the phosphate pegmatite at Hagendorf Sü d, Bavaria, Germany. Synchrotron X-ray data were collected from a 3 mm diameter fibre and refined in space group P1 to R 1 = 0.054 for 1484 observed reflections. The refinement confirmed the results of chemical analyses which showed that one quarter of the trivalent iron in the strunzite crystals is replaced by aluminium. The paragenesis revealed by scanning electron microscopy, in combination with chemical analyses and a crystal-chemical comparison of the strunzite and jahnsite structures, are consistent with strunzite being formed from jahnsite by selective leaching of (100) metalÀphosphate layers containing large divalent Ca and Mn atoms.

Zeolitic water in strunzite-group minerals

“…The H-bonding scheme is given in Table 6. It is similar to that reported for Al-bearing strunzite (Grey et al ., 2012) with the exception of bonds associated with Ow4. In Al-bearing strunzite, which has no zeolitic water, Ow4 does not participate in any H-bonding with bonds shorter than 3.0 Å, whereas in ferrostrunzite, Ow4 acts as a donor to Ow7 with a relatively short Ow4−Ow7 distance of 2.73 Å.…”

“…The structural results reported here, together with those reported for zincostrunzite from two localities, as well as for Zn-bearing ferristrunzite from Hagendorf Süd (Kampf et al ., 2017; Grey et al ., 2017) are all consistent with zeolitic water being an integral component of strunzite-group minerals. The only exception, out of nine separate structure refinements, is the Al-bearing strunzite from Hagendorf Süd (Grey et al ., 2012). This may be related to the formation of the Al-bearing strunzite as an alteration of jahnsite, involving selective leaching of large divalent cations from the jahnsite structure, which itself does not contain zeolitic water.…”

“…The TwinSolve program within the Rigaku CrystalClear software package was used for processing the structure data for the twinned strunzite crystals, including the application of an empirical multi-scan absorption correction using ABSCOR (Higashi, 2001). The atom positions for Al-bearing strunzite (Grey et al ., 2012) in space group were used as the starting point for the structure refinements, which employed SHELXL-2013 software (Sheldrick, 2015). For ferristrunzite and ferrostrunzite, scattering factors for Fe were used for the three independent metal atom sites.…”

“…(1978) suggested that this was due to the lack of zeolitic water in the interlayer region in strunzite. A recent structure refinement of Al-bearing strunzite from Hagendorf Süd also found no evidence for zeolitic water, despite having diffraction data of high-enough quality to locate all the H atoms (Grey et al ., 2012).…”

Crystallographic ordering of aluminium in laueite at Hagendorf-Süd

“…Studies on Al 3+ /Fe 3+ mixing in pegmatitic secondary phosphate minerals can provide valuable information on the reaction conditions that prevailed and on likely precursor phases in the pegmatite. For example, in our recent study on Al-bearing strunzite (Mn,Fe) 2+ (Fe,Al) 3+ 2 (PO 4 ) 2 (OH) 2 •6H 2 O, from the Cornelia mine, Hagendorf Süd, the quantification of Al incorporation at the Fe 3+ sites provided key information for the development of a paragenesis mechanism whereby strunzite formed from Al-bearing jahnsite by selective leaching of divalent cation phosphate layers (Grey et al, 2012). In this present paper we report the extension of these studies to the case of Al incorporation in laueite, Mn 2+ Fe 3+ 2 (PO 4 ) 2 (OH) 2 •8H 2 O, at Hagendorf Süd.…”