\ I 7'1,71 ¡1 :), THE CRYSTAL STRUCTURE OF THE MINERAL SCHOLZITE AND A STUDY OF THE CRYSTAL CHEMISTRY OF SOME RELATED PHOSPHATE AND ARSENATE MINERALS A thesis submitted for the Degree of Doctor of PhilosoPhY at the University of Adelaide in April, 1975 by R0DERICK JEFFREY HILL, B.Sc. (Hons.) Department of Geology and Mineralogy Au/¿tr¡'t ,,! /'/,".'','-'"' ' TABLE OF CONTENTS Page SUMMARY (i) STATEMENT OF ORIGINATITY (ii) ACKNOWLEDGEMENTS (iii) GENERAL INTRODUCTION I CHAPTER 1 TIIE GEOI.OGY AbID MINERALOGY OF REAPHOOK HILL, SOUTTI AUSTR.ALIA 2 1.1 ABSTR,ACT 2 r.2 INTRODUCTTON 2 1.3 GEOIÐGICAL SETTING 3 I.4 EXPERTMENTAI TECHNIQT ES 5 1.5 THE MAJOR PHOSPHATE MTNERALS 6 1.5.1 Tarbuttite - Znr(po4) (OH) 6 1.5.2 Parahopeite ZnrZn(pOn) - Z.4HZo 9 I.5.3 Scholzite CaZnU(pO4) - 2.2H2O 9 1.5.4 Zincian Collinsite Car(Mg,Zn) (pO4) - 2.2H2O 15 1.6 ASPECTS OF EHE CRYSTA¡ CHEMISTRY OF THE MAJOR PHOSPHATE MINERALS 19 L.7 PARAGENESIS 23 1.7.1 Major Minerals 23 L.7.2 Other lvlinerals 26 1.7.3 Conclusions 27 CHAPTER 2 TIIE CRYSTAI STRUCTURE OF SCHOLZITE 30 2.L ABSTRACT 30 2.2 INTRODUCTION 32 2.3 DATA COLLECTION AND ÐATA REDUCTION 32 2.4 DISCUSSION OF TITE INTENSITY DISTRIBUTION 35 2.4.L Subcell Structure and pseudosynunetry 35 2.4.2 Dete::mination of the True Syrnmetry 4L 2.4.3 Structural Disorder 4l 2.5 STRUqrURE SOLUTION AND REFINEMENT OF THE AVER.AGE ST'BCELL 52 2.6 DESCRIPTION AND DISCUSSION OF THE AVERAGE ST]BCELL STRUCTURE 60 2.6.I Topology 60 2.6.2 Disorder 65 2.6.3'iThermal" parameters 67 2.7 STRUCTURE SOLUTION AND REFTNEMENT OF TITE },IAIN CELL 68 2.7.I llethod of Successive Àpproximations 69 2.7.2 Optirnisation of Interatomic Distances 85 2.7.3 Refinement in Space Group n'rî 96 2.8 STRUCTURE FIGURES AIID TABI,ES 99 2.9 DTSCUSSION OF THE I\4AIN CELL STRUCTURE 105 2.9.L Topology r05 2.9.2 Structural Disorder 107 2.9.3 Possibilities for Further Work LL2 2.LO CONCLUSIONS ll3 CHAPTER 3 THE CRYSTAT STRUCTURE OF HOPEITE: Zna(PO ) 4H o 115 4 2 2 3.1 ABSTRACT 115 3.2 IIüTRODUCTION 115 3.3 DATA COLI,ECTION AND DATA REDUETION 117 3.3.1 Cl,tK c Data Co1lecÈion 119 3 3.2 MoK Data Collection ct L20 3 3.3 Data Reduction L22 3.4 STRUqrURE SOLUTION A}TD REFINEMENT 124 3.4.1 Mo Dat-a Refinement l-24 3.4.2 Cu Dat-a Refinement 139 3.5 STRUCTURE FIGURES AND TABLES 143 3.6 COMPARTSON OF THE T!.TO MODELS 148 3.7 DTSCUSSION ].49 3.7.1 Description of the Structure r49 3.7.2 Structure Analogues 152 CHAPTER 4 THE CRYSTAI STRUCTURE OF PHOSPHOPHYLLITE, (Po4) 155 znr(Fe,Mn) 2. 4H2o 4.r ABSTRACT 15s 4.2 INTRODUCTION 155 4.3 T'NIT CELL DIMENSIONS AND CONTENTS 1'57 4.4 CRYSTA], STRUCTURE EXPERIMENTS 160 4.4.L Distance Least Squares Refinement 161 4.4.2 Powder Diffraction Analysis 168 4.5 STRUCTURE ANAIOGI.'ES 173 4-6 CONCLUSIONS r80 CHAPTER 5 TIIE CRYSTAI STRUCTURE OF ADAI4ITEI ZnU(AsOn) (OH) 181 5.1 ABSTRACT 181 5.2 INTRODUCTTON 181 5.3 DATA COLLECTION AND DATA REDUCTION 183 5.4 STRUCTURE SOLUTION AND REFINEMENT 19r 5'.5 STRUCTURE FIGURES AND TABLES 204 5.6 DESCRIPTION AND DISCUSSION OF THE STRUCTURE 208 5.6.1 Topology 208 5.6.2 Structure Analogues 2IO 5.7 PENTACOORDINATION 2LL 5.7. I General Discussion 2Lt 5.7.2 Pentacoordinated Zinc 2L4 CHAPTER 6 PHOSPHATE SYNTHESÏS 2L8 6.1 ABSTRACT 2L8 6.2 INTRODUCTION 218 6.3 EXPERIMENTAI METHODS AIID RESULTS 2L9 6.4 MORPHOLOGY, X-RAY AND THERMAL CHARACTERISTICS OF TTIE SYNTHETIC MINER,ATS 225 CaZnr(PO4) 225 6.4.I Scholzite ' 2-2H20 6.4.2 Hopeite - Zo3(PO4) 2- HZO 231 6.4.3 znr(Pon) r.2Hzo 236 6.5 CONCLUSTONS 236 CHAPTER 7 THERMAL AD{ALYSIS 239 7¿L ABSTRACT 239 ?.2 INTRODUCTION 239 7.3 METTTOD AI{D APPARATUS 240 7.4 RESULTS AND DTSCUSSION 244 CaZnr(PO 244 7.4.L Natural Scholzite - 4) 2.2H2o 7.4.2 Slmthetic Scholzite 249 4H o 250 7.4.3 Natural Hopeite - Zn3eo')2- 2 7.4.4 Slmthetic HoPeite 254 (Poo) 258 7.4.5 zn, 2.2H2o Znr,Zn(POr) 258 7.4.6 ParahopeiEe - 2.4H2O (Po4) 262 7.4.7 Zincian Collinsite - Ca, (M9O S6,zla'.43) Z-2H2o 7.4.8 Tarbuttite - Znr(PO4) (OH) 263 7.4.9 Adamite, h2(Ason) (OH) 263 7.5 CONCLUSIONS 265 ChAPTER 8 INFRARED ABSORPT]ON SPECTROSCOPY 267 26? 8.1 ABSTR,ACT A.2 INTRODUCTION 267 8.3 THEORY 2?O A.4 EXPERIÌ,IENTAL METHOD 27r 8.5 SPECTRAL ASSIGNMENTS 272 8.6 RESULTS AND DISCUSSTON 273 8.6.1 Scholzite CaZnr(PO4) - 2.2H2O 273 Zincian Ca (Pol 2H20 280 A.6.2 Collinsite - ,(t49,zn) , 8.6.3 Hopeite - Zn PO 4rzo 284 3 4 ¿ 8.6.4 Parahopeibe ZnrZn(POn) - Z.AHZ 289 8.6.5 Tarbuttite - Znr(PO4) (OH) 292 8. 6.6 Adamite - ,n2(AsOn) (OH) 297 8.7 CONCLUSIONS 299 8.8 SHORT LIST OF REFERENCES 302 CHAPTER 9 SUMMARY AND CONCLUSIONS 303 APPENDIX I COMPUÎER PROGRAM ST]M}4ÃRY A.t APPENDIX IT REDUCTTON OF PHOTOGRAPHIC DATA A.4 (a) AUFAC A.5 (b) AULAC A.6 APPENDTX ITI DIFFRACTOMETER DATA COLLECTION AI{D REDUCTION A.8 (a) Buerger-Supper Equi-inclination x-ray Diffractometer A.8 (b) Stoe Equi-inclination X-ray Diffractometer A.11 APPENDIX IV CRYSTAI STRUCTURE REFINEMENT A.17 (a) STRUCTURE FACTORS A.17 (b) TNTERATOIVITC DISTANCES A.20 APPENDIX V PROGRAM PI,ANE A.22 APPENDIX VI TABLES OF STRUCTURE FACTOR DATA A.25 BIBLIOGRAPHY SUMMÀRY This thesis has concentrated on the investigation of the x-ray crystal structure of three minerals (namely scholzite, hopeite and adamite), with supplemenÈary inforrnation being supplied by electron probe micro-analysis, sythesis, thermal dehydration and. infrared absorpÈion spectroscopy. The solution of the crystal structure of scholzite presents a nu¡nber of interesting, if not unique, problems, caused mainly by the presence of a three-fold sr:bstructure parallel to b*, and quite severe one-dimensional stacking dísorder parallel Eo ax. Pseudosymmetry produced by the trans- lational periodicity is further complicated by the fact that the heavy atoms lie in special positions within the unit cell, necessitating the use of a number of unconventional techniques (e.9. steric hindrance, successive approximations and optimisation of interatomic distances) during refinement. The results of this study indicate that the atomic displacements from ideal, high syruneÈry positions responsible for the superstructure diffrac- tion,effects are of comparable magrnitude to the r.m.s. amplitude of thermal vibration. The one-dimensional disorder is interpreted, on the basis cf x-ray and thermal dehydration experiments, as arising due to the presence of stacking faults paralle1 to (100) passing through the planes of Ca (H,o) octahedra zon in the unit cell. The atomic framework of the mineral hopeiÈe has been refíned using two sets of diffractometer-collected x-ray diffraction intensities. These experiments indicate the existence of a unique non-hydrogen atom architecture, but thermal dehydration and infrared. absorption stud.ies de¡nonstrate the presence of a number of different modifications as sub- microscopic intergrowths in both natural and synthetic material. These forms differ only in the nature of the hydrogen bonding schemes and are formed during crystal growth as a result of slight fluctuations in pH ard/or temperature. The crystal structure of the mineral adamite, containing Zn in both five-and six-fold coordination, has been determined by Direct tlethods. The infrared absorption frequencies of the ZnOU group are discussed in relaÈion to those of equivalent groups in tarbuttite, its phosphate analogue. (i) The assistance and guidance given to the author by various people are detailed in the acknowledgements. Except where otherv¡ise indicated, all results and conclusions presented in this thesis are those of the author. R.iI. HILL April, 1975 (ii) ACKNOWLEDGEIVIENTS I express sincere tha¡ks to my supervisor, Dr. J.B. Jones, for his advice, interesÈ and encouïagement throughout the duration of ttris research. Special thanks are due to Dr. A.R. Milnes (Department of Earth Sciences, Monash University) for his collaboration and assistance in many aspects of the thesis. Dr. A.fù. Kleernan gave freely of his experience and knowledge at atl times and read the final draft of the manuscript. I also wish to record my thanks to Dr. M.R. Snow (Department of Physical and Inorganic Chenr-istry, University of Adelaide) for numerous helpful d.iscussions on many of the problems of crystal structure analysis. I am indebted to a number of persons for making available facilities at various stages of the.research. Notable anrong these are Dr. M.R. Taylor of the School of Physical Sciences, the Flinders University of South Australia (one diffractometer data collection); Dr. E.R. Segnit of Division of Mineral Chemistry, C.S.I.R.O. (thermal and infrared analyses); Irlr. Irl. Raupach of Chemistry Section, Division of Soils, C.S.I.R.O. (infrared analyses); Dr. F. Lawson of Department of Chemical Engineering, Monash University (thermal analyses); Dr. K. Norrish of Division of Soils' C.S.f .R.O. (electron probe microanalyses) . I am especially grateful to l4r. M.J. Fitzgerald for innumerable hours of fruitful discussion on many aspects of the thesis; to Mr.