Georgeite and azurite as precursors in the preparation of co-precipitated copper/zinc oxide catalysts

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1 Applied Catalysis A: General, 85 (1992) l-11 Elsevier Science Publishers B.V., Amsterdam APCAT 2268 Georgeite and azurite as precursors in the preparation of co-precipitated copper/zinc oxide catalysts A.M. Pollard, M.S. Spencer, R.G. Thomas, P.A. Williams2 School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O. Box 912, Cardiff CFl3TB (UK) and J. Holt and J.R. Jennings ICI Chemicals and Polymers Ltd., Research and Technology Department, P.O. Box 90, Wilton Centre, Middlesbrough, Cleveland TS6 8JE (UK) (Received 30 January 1991, revised manuscript received 20 March 1992) Abstract Georgeite, a recently identified basic copper carbonate mineral, can be synthesised in aqueous solutions from copper salts. It has now been shown that a zincian georgeite (i.e. georgeite with some substitution of copper by zinc) is formed by precipitation with sodium carbonate in copper-zinc systems. Conversion of zincian georgeite to a malachite phase in an aqueous medium occurs more slowly than the equivalent conversion of pure copper georgeite. The possibility of georgeite formation as a precursor to malachite in the manufacture of copper/zinc catalysts is discussed: it is suggested that the blue/green colour transition seen during the ageing of precipitated copper/zinc catalyst precursors can be attributed to the conversion of georgeite to malachite. Synthetic azurite materials, with and without zinc inclusion, were prepared from aqueous suspensions of georgeite with azurite seeding under 40 bar carbon dioxide. These were used as precursors to prepare active copper/zinc catalysts but their performance was inferior to that of a conventional catalyst. Keywords: aurichalcite, azurite, georgeite, malachite, catalyst preparation, catalyst precursors, precipitation, copper/zinc oxide, methanol synthesis. INTRODUCTION Copper/zinc oxide catalysts are widely used in the chemical industry for methanol synthesis, the water-gas shift reaction and various hydrogenations. Correspondence to: Professor MS. Spencer, School of Chemistry and Applied Chemistry, University of Wales College of Cardiff, P.O. Box 912, Cardiff CF13TB, UK. Tel. ( ) , fax. ( ) Now at Department of Archaeological Science, University of Bradford, Bradford BD7 ldp, UK. 2No~ at Department of Chemistry, University of Western Sydney, Nepean, P.O. Box 10, Kingswood, NSW 2747, Australia /92/$ Elsevier Science Publishers B.V. All rights reserved.

2 2 A.M. Pollard et al./appl. Catal. A 85 (1992) l-l 1 These catalysts are usually manufactured by co-precipitation [l-4], typically from a solution of copper, zinc and other nitrates with a solution of sodium carbonate, followed by calcination and reduction of the precursor to give the active catalyst. The precursors which give optimum catalysts contain various basic copper and zinc carbonates and many of the large number of known carbonates have been found in catalyst precursors [l-12]. Catalysts for methanol synthesis and some hydrogenation reactions have high copper/zinc ratios. Catalyst precursors with Cu/Zn ratios in the range 100/O to 50/50 have been studied in detail by Porta et al. [9,10], Waller et al. [ 111 and Waller and Stone [ 121. Both groups agree that at low zinc concentrations ( < 15% ) zincian malachite, ( Cu2_,ZnY) ( CO3 ) (OH )2, is precipitated but that at higher zinc concentrations aurichalcite, (Cug_-xZnx) (CO,),(OH),, and occasionally hydrozincite are also formed. On ageing this precipitate the aurichalcite disappears and malachite of higher zinc concentrations (up to about 30% ) is formed. The properties of the resulting catalysts can be understood [ 111 in terms of these materials and changes in the precursor material. Nevertheless two difficulties remain. Many workers [ 6,7,9,10,13] with precipitates over a wide range of compositions have described a change in colour from blue of the initial precipitate to a green or blue-green of the aged material. Clearly the colour of the aged material corresponds well to malachite or malachite/aurichalcite mixtures but the initial blue colour indicates the possibility of other reactions occurring during the earliest stages of ageing. Further, some early attempts [ 141 to identify the initial precipitate by X-ray diffraction showed the presence of amorphous material only. Recently the mineral georgeite, Cu,CO, ( OH)2, a blue basic copper carbonate which is an analogue of malachite but amorphous by X-ray diffraction, has been characterised and synthesised in the laboratory by Pollard et al. [ 151. Georgeite is a possible candidate for the catalyst precursor as it is made by carbonate precipitation and it transforms to malachite if left in contact with the mother solution. However it was not known whether georgeite is formed in precipitations typical of catalyst preparations, i.e., from concentrated solutions at 60 to 90 C and with zinc ions present in solution. In this paper we report some initial results with copper/zinc systems which show that georgeite is indeed formed under these conditions. The changes occurring during the ageing of the precursors of Cu/ZnO/A120, catalysts may be more complex than had been realised before. Azurite, a natural copper hydroxycarbonate (Cu, (CO,), (OH) 2 ), can also be synthesised in aqueous systems. Thus the preparation of azurite may provide another potential method for the manufacture of copper/zinc catalysts, as an alternative to the conventional malachite- or aurichalcite-based routes. Unlike most other copper hydroxycarbonates, natural azurite does not display any tendency for copper to be replaced by zinc or other divalent cations, but it is possible that some incorporation or intermixing of zinc may occur in the

3 A.M. Pollard et al./appl. Catal. A 85 (1992) l-11 3 preparation of synthetic microcrystalline azurite. The resulting zinc distribution might be sufficient for synthetic azurite to be a suitable precursor for copper/zinc catalysts. There is a good correlation between the activity of copper/zinc catalysts and copper metal surface area [ , so high activity in these catalysts is achieved by the preparation of a high dispersion of copper. Preliminary results reported here indicate that there was some incorporation of zinc in a synthetic azurite. This azurite precursor gave an active catalyst, although its performance was inferior to that of a commercial catalyst. EXPERIMENTAL Georgeite preparation In a series of experiments, 50 cm3 of a 0.1 M aqueous solution of CuSO, was added rapidly to 100 cm3 of a stirred 1.0 M aqueous solution of Na,CO, at 60 C (i.e. by reverse batch precipitation). A rapid reaction ensued, accompanied by the liberation of gaseous carbon dioxide and resulting in the formation of a blue precipitate. This solid was immediately collected at the pump on a glass frit, washed with cold water, then acetone, and dried in vacua over silica gel at room temperature. This procedure was used to minimise transformations during sampling. In a second series of experiments, an aqueous solution was made 0.1 M with respect to CuS04 and 0.03 M with respect to ZnS04. Sulphate salts were used in these preparations partly for convenience and partly to minimise the probability of formation of basic salts other than hydroxycarbonates. It was not intended to use these preparations to make catalysts, so traces of residual sulphate (see below) did not cause any subsequent difficulty. A 50-cm3 aliquot of this solution was added to 100 cm3 of 1 M aqueous Na,C03 solution at either 25 or 60 C. The same reaction sequence was observed as above for solutions containing no Zn2+ (aq) ions. The resulting blue precipitate was isolated at the pump in the same manner as described above. Samples of mineral georgeite came from North Wales and Australia, and synthetic malachite and georgeite for comparison were prepared by precipitation at 298 K, as described before [ 151. Azurite preparation Azurite is not easy to prepare [ 201. It is less stable and has a higher carbonate content than malachite, so a high partial pressure of carbon dioxide is necessary to control the ageing stage. However, even at 40 bar carbon dioxide pressure, azurite was not obtained unless the amorphous precursor gel had been seeded with either natural or synthetic azurite. In a typical experiment, a 1.5-molar excess of a 0.5 M aqueous Na,CO, solution was added at ambient

4 4 A.M. Pollard et al./appl. Catal. A 85 (1992) 1-l 1 temperature to a 0.5 M aqueous CU(NO~)~ solution contained in a one-litre rocking autoclave, equipped with a high-pressure supply of carbon dioxide. Natural azurite, crushed to a mean particle size of approximately 0.1 mm was added to the mixture and the autoclave sealed. Carbon dioxide was introduced to a total pressure of 40 bar and the mixture heated to 50 C for 5 h. On discharge, an intensely deep blue slurry was obtained and the solid product (identified as azurite by X-ray diffraction) was separated by conventional filtration and water washing. The azurite product was calcined in air at 350 C, as is typical for copper catalysts for methanol synthesis, before tests for catalytic activity. In similar experiments, various amounts of zinc nitrate were added to the copper solution before reaction, so as to make copper/zinc products. The maximum amount of zinc added in this way was 30% of the total copper content. A similar deep blue product was obtained, but in this case the solutions with the higher levels of zinc gave some aurichalcite and sodium zinc carbonate (almost impossible to remove by water washing without the destruction of the azurite) as well as the azurite. Characterisation of hydroxycarbonates Infrared spectra of the products from the georgeite preparations were run in KBr discs using a Perkin Elmer 783 spectrophotometer. The X-ray powder diffraction patterns of the solid products were checked using a Debye-Scherrer camera of mm diameter and Cu Ka! radiation. Thermogravimetric analyses, accurate to O.l%, were carried out using a Stanton Redcroft TG750 thermobalance. The results of these analyses were then compared with those of synthetic and natural georgeite and malachite obtained previously [ 151. Catalyst activity tests Calcined products were tested for methanol synthesis activity using a conventional microreactor system. In situ reduction was performed with 5% HZ/ 95%N2 at 150 C for 24 h. The use of low hydrogen partial pressure and low reduction temperature minimised the risk of copper sintering due to a reduction exotherm, either during activation or subsequent catalytic reaction. Other work [ 211 with conventional copper/zinc preparations has shown that 90% of the final copper area can be formed by reduction at 150 C. After activation the reduction gas was replaced by synthesis gas (3%C0,/10%C0/67%H2/20%N~). The methanol content of the synthesis gas was measured at steady state after passing over the catalyst at 30 bar total pressure, 250 C, and a space velocity of h-l. Some further development of copper surface and possibly some copper sintering [ 221 could be expected under these conditions. Repeat tests on the same catalyst gave methanol analyses reproducible to 0.5%.

5 A.M. Pollard et al./appl. Catal. A 85 (1992) l-l 1 5 RESULTS AND DISCUSSION Georgeite preparation The blue materials isolated in the syntheses described above, with or without Zn2+ in the reaction mixture, were identified as georgeite from IR spectra (Fig. 1 ), thermogravimetric analyses (TGA) (Table 1) and lack of any X-ray powder diffraction pattern. Clearly georgeite is the initial product in carbonate precipitations from copper-containing solutions over a wide range of conditions. No X-ray pattern corresponding to any zinc compound was found and the IR spectra of the pure copper and zinc-containing products were identical.the IR spectrum for malachite (Fig. 1) agrees well with that reported by Waller et al. [ 111. It should be noted that the type georgeite specimen analyzed by Bridge et al. [ 231 was found to contain 0.6% zinc. It is possible that zinc is present as a mixture of X-ray amorphous georgeite and an X-ray amorphous zinc hydroxide. If so, the hydroxyl and carbonate bands in the IR spectra must 4am xc0 mn 13X lax, 400 -/on- Fig. 1. Infrared spectra of (A) natural georgeite, ex Britannia Mine, North Wales, UK [ 151; (B) natural georgeite, ex Carr Boyd Mine, Western Australia [ 151; (C) synthetic copper georgeite, prepared at 25 C [ 151; (D ) synthetic zincian georgeite, prepared at 60 C; (E ) synthetic copper georgeite, prepared at 60 C; (F) synthetic copper malachite, from recrystallisation of synthetic georgeite.

6 6 A.M. Pollard et al./appl. Catal. A 85 (1992) l-l 1 TABLE 1 Analytical results for synthetic georgeite samples Component (wt.-%) Sample d cue Cb,Zn,.,,O CO, Hz a Synthetic georgeite. b Calculated for Cu,C03 (OH ) 2. Synthetic zincian georgeite. d Calculated for (Cu,.,,Zn,.,,),CO,(OH),. be coincident with those of georgeite. The IR spectra and X-ray patterns also show that neither malachite nor aurichalcite is present. It is more likely that a solid-solution series involving zinc and copper is present for georgeite. Zinc-free samples of georgeite recrystallise readily on standing in contact with the mother liquor at ambient temperatures, but zinc-containing samples react more slowly. Thus a sample of georgeite, formed using a 70:30 solution of Cu2+ (aq):zn2+ (aq) ions and isolated after having been left to stand in contact with its mother liquor at 20 C for two weeks, was found to consist only of georgeite. Similar experiments using solutions that contained only Cu2+ (aq) ions yielded either malachite or chalconatronite within 24 h, depending on whether the reaction mixture was stirred or not [ 151. The increased stability of georgeite in the zinc-containing preparations is further evidence that at least some zinc is incorporated in the georgeite lattice. There is strong evidence [8,9,11] that zincian-malachite is more stable than pure copper malachite at ambient temperatures: this is due to increased covalent metal-oxygen bonding as is reflected in the decreased unit cell parameters. The comparative stabilities of pure and zincian georgeite found here fits the same pattern. Azurite preparation The products from the azurite preparations, after filtration, washing with water and drying, were analyzed by X-ray diffraction. The zinc-free product gave a diffraction pattern in good agreement with standard data for azurite. Two changes resulted from the addition of zinc to the reaction mixture. Azurite was still the major product but there was some evidence of incorporation of zinc in the azurite lattice from the small shift in the (211) line. Further, the product from reaction mixtures with higher levels of zinc also contained some

7 A.M. Pollard et al./appl. Catal. A 85 (1992) l-l 1 7 aurichalcite and sodium zinc carbonate, as revealed by their X-ray diffraction patterns. The initial product formed on mixing the solutions in the autoclave was probably georgeite, in view of the results above showing that georgeite is formed in copper/sodium carbonate precipitations under a wide range of conditions. If so, the georgeite recrystallised, either directly or via other phases, to azurite in the autoclave (with 40 bar carbon dioxide and azurite seeds). This transformation has not been reported before but it appears to be possible from the relative instability of georgeite. The apparent incorporation of zinc into azurite is surprising in view of the lack of cation substitution in natural azurite. Possibly this is achieved because the azurite precursor is zincian georgeite, thus providing the most favourable circumstances for zinc substitution in azurite. However the formation of other zinc compounds, aurichalcite and sodium zinc carbonate, at the higher zinc levels used (up to 30% substitution) suggests that even if a zincian azurite is formed, the upper limit of zinc incorporation is well below 30%. Catalyst preparation Neither the georgeite nor the azurite preparations were carried out in exactly the same way as the production of commercial copper/zinc/alumina catalysts, particularly as these are usually made [l-4] by continuous co-precipitation at constant ph rather than as the batch precipitations used in this work. Further, none of our preparations contained the alumina essential for a commercial catalyst. There must therefore be some doubt about the relevance of our work to commercial catalyst production. Nevertheless the zinc/copper ratio, reagent concentrations and precipitation temperature used in the georgeite preparations were typical of commercial practice. It is clear that georgeite is formed as a precursor to malachite in carbonate precipitations over a wide range of precipitation conditions. As georgeite is also formed when zinc is present in the precipitating solutions it is probable that the blue solid usually seen as the initial material in the preparation of copper/zinc oxide/alumina catalysts is georgeite. The comparative stability of zincian georgeite is qualitatively in accord with observations on catalyst preparation. Porta et al. [ 91 reported the time from precipitation to the blue-green transition to be min at C. The failure of earlier workers to identify georgeite can be attributed to two causes. First, zinc-free georgeite is unstable in contact with the precipitating solution, even at 25 C, and transforms to malachite [ 151. Zincian georgeite is more stable but recrystallisation to other hydroxycarbonates occurs at typical catalyst preparation temperatures (60-80 C ). Thus in experiments when the precipitate was aged before sampling [6,7,9,10] the material found was malachite and other basic carbonates more stable than georgeite. Waller et al.

8 8 A.M. Pollard et al./appl. Catal. A 85 (1992) l-11 [ 111 sampled the precursor immediately after precipitation but without the quenching technique employed here. It is unlikely that any georgeite would have remained in the sample after filtering and washing at ambient temperature or above, followed by drying for 16 h at 90 C. Sampling without quenching is thus equivalent to accelerated ageing. Waller et al. [ll] proposed a reaction scheme for the ageing in the 2:l Cu/ Zn catalyst system in which two mineral phases, low-zincian malachite and high-zincian aurichalcite, recrystallised to give high-zincian malachite as the end product of ageing. We now propose (Fig. 2) an additional precursor stage involving zincian georgeite formation and recrystallisation to the mala- 2:1 Cu/Zn nitrate aqueous solution I precipitation blue zincian georgeite 2:l Cu/Zn ageing CO2 I blue-green low-zincian malachite 85:15 CuJZn + high-zincian aurichalcite 60:40 CuJZn ageing 1 blue-green high-zincian malachite 2:1 Cu/Zn drying, calcination reduction CuJZnO catalyst Fig. 2. Proposed reaction scheme (extended version of earlier scheme [ 111) for the precipitation, ageing and subsequent stages in the preparation of 2:l Cu/Zn catalysts.

9 A.M. Pollard et al./appl. Catal. A 85 (1992) l-l 1 9 chite/aurichalcite mixture. This does not affect the arguments presented before [ 111 for the subsequent ageing. This scheme also accounts for an apparent discrepancy between the model system of zinc-free georgeite conversion to malachite and commercial copper/zinc/alumina catalyst manufacture. Carbon dioxide is evolved copiously in the initial precipitation stage in both systems. The conversion of georgeite to malachite proceeds without further carbon dioxide evolution and this is because both georgeite and malachite have the same chemical formula, CuJ!O, (OH) 2. However, carbon dioxide evolution is observed [9,10] at the blue-green transition during commercial catalyst preparation. In the presence of enough zinc both malachite and aurichalcite are formed (Fig. 2) and carbon dioxide evolution would be expected to be associated with this step. The ( C03): (Cu + Zn) ratio in both malachite and georgeite, from the formula above, is 0.50 whereas the chemical formula of aurichalcite, (Cu5_xZnx) (CO,), (OH),, gives a value of 0.40 for the same ratio. Thus the formation of aurichalcite as a co-product leads to overall loss of carbonate and consequent carbon dioxide evolution. Both Porta et al. [lo] and Waller et al. [ 111 have shown that the final malachite product is of uniform composition, both with respect to different crystals and through the crystals. As this is formed in the 2:l Cu/Zn system from two mineral phases, low-zincian malachite and high-zincian aurichalchite, Waller et al. [ 111 suggested that the high-zincian malachite end product was formed via solution and re-crystallisation rather than via a solid-state transformation. They attributed the driving force for these transitions during ageing to the greater stability of high-zincian malachite over low-zincian malachite, even for the smaller crystal size of the high-zincian malachite. This argument still stands but there is now the additional driving force of the georgeite-malachite conversion for the overall ageing process. Earlier work [ 151 has shown that georgeite can recrystallise to malachite or chalconatronite, depending on experimental conditions. It now seems likely that conversion (direct or indirect) to azurite or aurichalcite is also possible under certain conditions. Catalyst properties Only the azurite products were converted into catalysts. The unaged precursors in conventional preparations are known [ 2,111 to give less active catalysts than aged precursors and, further, any catalysts made from the georgeite products in this work were likely to be poisoned by traces of sulphur derived from residual sulphate. In preliminary experiments catalysts made from the azurite products were tested for methanol synthesis activity using a conventional microreactor system and the results are given in Table 2. No copper metal surface areas were measured. The catalyst derived from zinc-free azurite was essentially inactive

10 10 A.M. Pollard et al./appl. Catal. A 85 (1992) l-l 1 TABLE 2 Activity tests on various copper catalysts Test conditions: synthesis gas (3%CO,/lO%CO/67%H,/2O%N~); ity, h- 30 bar; 250 C; gas space veloc- Catalyst type Copper content Exit methanol (% CUO) concentration (mol-%) Cu/ZnO/Al,O, 60 via malachite cu 100 via azurite Cu/ZnO 85 via azurite 4.1 <O.l 1.3 but the equivalent catalyst containing 15% zinc produced 1.3% methanol, which may be compared with about 4.0% from a typical conventional, malachitebased catalyst tested in a parallel microreactor tube. The zinc-free azuritebased catalyst contained no refractory oxide to prevent sintering of copper metal crystallites, so very low copper surface areas and very low catalytic activities would be expected [ Although the activity of the catalyst based on zincian azurite was lower than that of commercial catalysts, two factors need to be taken into account. First, the azurite-based catalysts did not contain alumina as a refractory support and this could have led to excess sintering of copper crystallites during the reduction and testing, giving low copper surface areas even in zinc-containing catalysts. Secondly, the azurite samples were prepared in a rocking autoclave which had no additional means of agitation. The crystallite sizes of the azurite which resulted were about 100 nm, more than double the size present in malachite-based catalysts. On this basis it is likely that technically an azurite-based process for the manufacture of methanol synthesis catalysts could be developed, giving catalysts equivalent to those obtained from malachite or aurichalcite routes. However, since there is no catalytic advantage to be obtained, the greater degree of complexity with the associated greater costs is such that azurite-based catalysts for methanol synthesis are most unlikely to achieve commercial acceptance. CONCLUSIONS 1. Georgeite, probably with incorporated zinc, is the initial product of the precipitation of an aqueous copper/zinc solution (Cu/Zn ratio= 3/l) with aqueous sodium carbonate solution over at least o C.

11 A.M. Pollard et al./appl. Catal. A 85 (1992) l Zincian georgeite is more stable in contact with its mother liquor than zinc-free georgeite. 3. Zincian georgeite is probably the initial precipitate in the commercial production of copper/zinc/alumina catalysts. 4. Synthetic azurite can be prepared from a precursor, probably georgeite, under 40 bar carbon dioxide and with azurite seeding. 5. Methanol synthesis catalysts made via synthetic azurite are more difficult to prepare and less active than commercial catalysts made by the malachite route. ACKNOWLEDGEMENT We wish to thank the SERC for financial support. REFERENCES L. Lloyd, D.E. Ridler and M.V. Twigg, in M.V. Twigg (Editor), Catalyst Handbook, 2nd Edition, Wolfe, London, 1989, p G.W. Bridger and MS. Spencer, in M.V. Twigg (Editor), Catalyst Handbook, 2nd Edition, Wolfe, London, 1989, p J.C.J. Bart and R.P.A. Sneeden, Catal. Today, 2 (1987) 1. G.C. Chinchen, P.J. Denny, J.R. Jennings, M.S. Spencer and K.C. Waugh, Appl. Catal., 36 (1988) 1. R.G. Herman, K. Klier, G.W. Simmons, B.P. Finn and J.B. Bulko, J. Catal., 56 (1979) 407. R.H. Hoppener, E.B.M. Doesburg and J.J.F. Scholten, Appl. Catal., 25 (1986) 109. E.B.M. Doesburg, R.H. Hoppener, B. de Koning, Xu Xiaoding and J.J.F. Scholten, in B. Delmon, P. Grange, P.A. Jacobs and G. Poncelet (Editors), Preparation of Catalysts IV, Stud. Surf. Sci. Catal., Vol. 31, Elsevier, Amsterdam, 1987, p M.H. Stacey and M.D. Shannon, in P. Basset and L. Dufour (Editors), Proc. 10th Intern. Symposium on Reactivity of Solids, Elsevier, Amsterdam, 1985, p P. Porta, S. de Rossi, G. Ferraris, M. Lo Jacono, G. Minelli, J. Catal., 109 (1988) 367. P. Porta, G. Fierro, M. Lo Jacono and G. Moretti, Catal. Today, 2 (1988) 367. D. Waller, D. Stirling, F.S. Stone and M.S. Spencer, Faraday Disc. Chem. Sot., 87 (1989) 107. D. Waller and F.S. Stone, in preparation. K. Tohji, Y. Udagawa, T. Mizushima and A. Veno, J. Phys. Chem., 89 (1985) N.H. Harbord, personal communication. A.M. Pollard, R.G. Thomas, P.A. Williams, P.Bridge and J. Just, Mineral. Mag., 55 (1991) 163. G.C. Chinchen, K.C. Waugh and D.A. Whan, Appl. Catal., 25 (1986) 101. G.C. Chinchen, P.J. Denny, J.R. Jennings, M.S. Spencer and K.C. Waugh, in preparation. R. Burch, S.E. Golinski and M.S. Spencer, Catal. Lett., 5 (1990) 55. G.C. Chinchen and MS. Spencer, Catal. Today, 10 (1991) 293. S. Hemar, Compt. Rend., 204 (1937) G.C. Chinchen and J.R. Jennings, European Pat. Appl (1988). G.C. Chinchen, M.S. Spencer, K.C. Waugh and D.A. Whan, J. Chem. Sot., Faraday Trans. 1,83 (1987) P.J. Bridge, J. Just and M.H. Hey, Mineral Mag., 43 (1979) 97.

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