Pezzottaite Chemical Formula

SpecialGem Edition MineralNew No.3 August 2004 THE CHALLENGE OF THE IDENTIFICATION OF A NEW GEMSTONE CHEMISTRY AND CRYSTALLOGRAPHY (NEW BERYL-GROUP MINERAL) MINERAL NAME: PEZZOTTAITE CHEMICAL FORMULA: Cs(Be2Li)Al2Si6O18 CRYSTAL SYSTEM: rhombohedral SPACE GROUP: R3c a = 15.946(2) Å b =15.946(2) Å c = 27.803(8) Å (a, b, c = unit-cell dimensions) α = 90° β = 90° γ = 120° (α, β, γ = angles of the unit-cell) V = 6122(2) Å3 (V = Volume of unit cell, Å = Ångstrom,1cm = 100 000 000 Å) Z = 18 (Z is number of formula units per unit-cell) NEW GEM MINERAL PEZZOTTAITE Caesium position Lithium position Lithium (Li) Caesium (Cs) inside channel inside oxygen tetrahedra Beryllium (Be) Silicon (Si) Aluminium (Al) Oxygen (O) Superstructure unit-cell ATOMIC ARRANGEMENTS MESSAGE Editor Message From The Editor’s Desk Dr. A. Peretti, FGG, FGA, EurGeol About 4000 mineral species are known and GRS Gemresearch Swisslab AG, P.O.Box 4028, 6002 about 20 to 30 new species are discovered Lucerne, Switzerland each year. The majority of the new species occurs as very small crystals and is only [email protected] detected with the help of very sophisticated optical and spectroscopic instrumentation Editorial Review Board available today. The discovery of a new mineral forming large crystal is thus Prof. Dr. B. Grobéty, Institute of Mineralogy and exceptional. Such a rare and spectacular Petrography, University of Fribourg, Fribourg, discovery of a new mineral with gem quality Switzerland was made in Madagascar. “Pezzottaite”, named after the Italian mineralogist Pezzotta, Prof. Dr. J. Mullis, Institute of Mineralogy and is a mineral belonging to the “beryl group”. Petrography, University of Basel, Basel, Switzerland The appearance of this beryl-like mineral on diverse Mineral shows (Tucson) attracted Prof. Dr. W. Oberholzer, Institute of Mineralogy and various research groups worldwide and two Petrology, Swiss Federal Institute of Technology groups identified almost simultaneously the (ETH), Zurich, Switzerland. material as a new mineral. The acceptance Former Curator of the Mineralogical Museum (ETH of a mineral as a new species requires the ZH). determination of a number of physical and chemical properties (optical character, Prof. Dr. K. Ramseyer, Institute for Geological Sciences, hardness, chemical composition, crystal University of Berne, Berne, Switzerland structure etc.). This "finger-print" has to be presented to the Commission on New Prof. Dr. D. Günther, Institute of Chemistry, Laboratory Mineral and Mineral Names (CNMMN), a for Inorganic Chemistry, ETH, Zurich, Switzerland body of the International Mineralogical Association (IMA), which has to approve this This journal follows the rules of the Commission on new mineral and its name. New Minerals and Mineral Names of the IMA in all matters concerning mineral names and nomenclature. This special “new gem mineral edition” of Contribution to Gemology No.3 gives an Distributor inside into the details of the physical and chemical analyses that were undertaken for GRS (Thailand) Co., LTD. the identification of the new gem mineral 257/919 Silom Rd., JTC Building, Bangkok 10500, “Pezzottaite” and the preparation of a Thailand. successful IMA application. Journal and Website Copyrighted by GRS Gemresearch Swisslab AG, Lucerne, Switzerland Adolf Peretti This report is published on-line at www.gemresearch.ch CONTENTS What's inside? Identifying a new gem mineral 1 Analyzing the crystal structure 1 The superstructure: The difference between the two minerals 2 “BERYL" and "PEZZOTTAITE" Materials 3 The application to the Commission on New Minerals and Mineral 3 Names (CNMMN IMA) Rotating pezzottaite crystal model 4 BOX 1 Chemistry and crystallography 4 Pezzottaite rough, cut and in matrix 5 BOX 2 Origin and mineralogy 5 BOX 3 Physical and optical properties 6 Chemistry of pezzottaite BOX 4A Electron microprobe analysis (EMPA) 7 BOX 4B Laser ablation mass spectroscopy analysis (LA-ICP-MS) 8 Crystallography of pezzottaite BOX 5A Single crystal X-ray diffraction analysis 9 X-ray powder diffraction analysis BOX 5B Relations to other mineral species 10 BOX 6 Miscellaneous 10 Inclusion features, literature and acknowledgments 11 Appendix Pezzottaite gemstone examples 12 The Identification of the New Gem Mineral Pezzottaite THE CHALLENGE OF THE IDENTIFICATION OF A NEW MINERAL SPECIES: EXAMPLE "PEZZOTTAITE" Adolf Peretti (1), Thomas Armbruster (2), Detlef Günther (3), Bernard Grobéty (4), Frank C. Hawthorne (5), Mark A. Cooper (5), William B. Simmons (6), Alexander U. Falster (6), George R. Rossman (7), Brendan M. Laurs (8) (1) GRS Gemresearch Swisslab AG, Hirschmattstr. 6, P.O. Box 4028, CH-6003 Lucerne, Switzerland (2) Chem. Miner. Kristallogr., University of Berne, Freiestr. 3, CH-3012 Berne, Switzerland (3) Laboratory of Inorganic Chemistry, ETH Hönggerberg, HCI, G113, CH-8093 Zurich, Switzerland (4) Department of Geosciences, University of Fribourg, Pérolles, CH-1700 Fribourg, Switzerland (5) Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada R3T 2N2 (6) Geology & Geophysics, University of New Orleans, New Orleans, Louisiana, LA 70148, USA (7) Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA (8) Gemological Institute of America, Carlsbad, CA 92008, USA (Authors (1)-(4) are referred in this article as the "Swiss research team" and authors (5)-(8) are referred in this article as the "US-Canadian research team" IDENTIFYING A NEW GEM MINERAL In 2002, a new gem mineral of commercial importance XRFanalysis - direct measurement by Laser Ablation was discovered. In accordance with the need for all Mass Spectroscopy was also used (see Box 4B and new mineral discoveries to be scientifically Fig. P16), as well as conventional methods used for characterized (see Nickel and Grice, 1998), the chemical analysis (Box 4A). In addition to challenges gemological community anxiously awaited the results in the analysis of chemical composition, determination of tests to positively identify the new mineral of different atomic positions in the crystal structure (Hawthorne et al., 2003, Hawthorne et al., submitted was not trivial. A combination of various analytical and Laurs et al., 2003). This period of analysis techniques was necessary (Figs. P3 and P17) to brought into play the question: EXactly what finally elaborate the structural differences to beryl procedures are necessary for the positive (Figs. P1 and P2 and Box 5B). It was discovered that characterization of a new mineral? the unit-cell of pezzottaite had unusually large dimensions, which is best described as a These principal steps of identification are illustrated in superstructure of conventional beryl (Figs. P1, P2 and the following case study for identifying a new mineral P6). Also, the number of atoms necessary to define of the beryl group - pezzottaite. the crystal structure turned out to be unusually high in comparison with other beryl- group minerals (Boxes 1 The identification of this new mineral provided two and 5). major challenges: first, the determination of the exact chemical composition, and secondly, the identification ANALYZING THE CRYSTAL STRUCTURE of its crystallographic structure (the geometrical arrangement of the atoms in three dimensions (see The secrets of the nature of a new mineral are so Box 1, Figs. P2 and P6). From special technique of small we cannot even identify them with the help of analysis (Boxes 4 and 5A), the exact stoichiometric microscopic magnification. One way to explore this chemical formula, and the space group of this new atomic world is with X-rays (Figs. P3 and P17). mineral, have to be determined (Box 1). As soon as the mineral was characterized (BoXes 1-6), the X-rays have a very short wavelength (with dimensions differences between already eXisting minerals had similar to atoms), allowing them to penetrate and also to be investigated (see Nickel and Grice, 1998 interact with atoms in a mineral structure. As atoms and Box 5B) and a decision had to be made regarding group together at very short distances, X-rays are whether a new mineral had been found, and, if so, diffracted when passing through a crystal and change what would be its new name? (Hawthorne et al., 2003 their direction when they interact with them. and Box 6). In the case of pezzottaite, these analysis Furthermore, diffracted X-rays interfere with each provided major challenges. As pezzottaite contains other, just like water waves emerging from two ships. diffraction pattern of a single crystal consists of Finally, the unit-cell and the space group can be light elements - such as hydrogen, lithium, and The interaction between atoms and X-rays depends, symmetrically arranged spots, where the spot determined (Boxes 1 and 5A). This is a crystallographic beryllium, which cannot be directly analyzed by among other factors, on the geometrical arrangement separation determines the periodicity of the lattice code that identifies the crystallographic nature of a quantitative methods commonly used for mineral of the atoms and can be interpreted with X-ray (unit-cell dimensions) and the arrangement of the mineral. analysis such as electron microprobe (EMPA) or diffraction diagrams, and computer calculations. A spots provides clues to the symmetry of the structure. 01 New Gem Mineral Species Pezzottaite: Comparison between Beryl and Pezzottaite THE SUPERSTRUCTURE: THE DIFFERENCE BETWEEN THE TWO MINERALS "BERYL" AND "PEZZOTTAITE" P1 P2 Fig. P1-2 Ball-and-stick models of beryl (Fig. P1) and pezzottaite

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