Proc. Natl. Acad. Sci. USA Vol. 94, pp. 12263–12267, November 1997 Geology Third-generation synchrotron x-ray diffraction of 6-mm crystal of raite, 'Na3Mn3Ti0.25Si8O20(OH)2z10H2O, opens up new chemistry and physics of low-temperature minerals (crystal structureymicrocrystalyphyllosilicate) JOSEPH J. PLUTH*, JOSEPH V. SMITH*†,DMITRY Y. PUSHCHAROVSKY‡,EUGENII I. SEMENOV§,ANDREAS BRAM¶, CHRISTIAN RIEKEL¶,HANS-PETER WEBER¶, AND ROBERT W. BROACHi *Department of Geophysical Sciences, Center for Advanced Radiation Sources, GeologicalySoilyEnvironmental, and Materials Research Science and Engineering Center, 5734 South Ellis Avenue, University of Chicago, Chicago, IL 60637; ‡Department of Geology, Moscow State University, Moscow, 119899, Russia; §Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, 117071, Russia; ¶European Synchrotron Radiation Facility, BP 220, 38043, Grenoble, France; and UOP Research Center, Des Plaines, IL 60017 Contributed by Joseph V. Smith, September 3, 1997 ABSTRACT The crystal structure of raite was solved and the energy and metal industries, hydrology, and geobiology. refined from data collected at Beamline Insertion Device 13 at Raite lies in the chemical cooling sequence of exotic hyperal- the European Synchrotron Radiation Facility, using a 3 3 3 3 kaline rocks of the Kola Peninsula, Russia, and the 65 mm single crystal. The refined lattice constants of the Monteregian Hills, Canada (2). This hydrated sodium- monoclinic unit cell are a 5 15.1(1) Å; b 5 17.6(1) Å; c 5 manganese silicate extends the already wide range of manga- 5.290(4) Å; b 5 100.5(2)°; space group C2ym. The structure, nese crystal chemistry (3), which includes various complex including all reflections, refined to a final R 5 0.07. Raite oxides in ore deposits and nodules from the sea floor and occurs in hyperalkaline rocks from the Kola peninsula, Rus- certain farming areas, the pyroxmangite analog of the lunar sia. The structure consists of alternating layers of a hexagonal volcanic metasilicate pyroxferroite, the Mn analog yofortierite chicken-wire pattern of 6-membered SiO4 rings. Tetrahedral of the clay mineral palygorskite, and the unnamed Mn analog apices of a chain of Si six-rings, parallel to the c-axis, alternate of sepiolite. in pointing up and down. Two six-ring Si layers are connected Historically, crystal chemistry began with the determination by edge-sharing octahedral bands of Na1 and Mn31 also of the atomic packings in centimeter to millimeter crystals of parallel to c. The band consists of the alternation of finite minerals such as halite and diamond some 80 years ago, using Mn–Mn and Na–Mn–Na chains. As a consequence of the primitive x-ray sources and detectors (Bragg era). It moved on misfit between octahedral and tetrahedral elements, regions to more complex structures in the 1920s and 1930s (era of of the Si–O layers are arched and form one-dimensional Pauling, Taylor, and other crystal chemists) as hot-cathode channels bounded by 12 Si tetrahedra and 2 Na octahedra. The x-ray machines became powerful enough for submillimeter channels along the short c-axis in raite are filled by isolated crystals. By the 1960s, new mathematical techniques coupled Na(OH,H2O)6 octahedra. The distorted octahedrally coordi- with the most intense laboratory x-ray sources and sensitive nated Ti41 also resides in the channel and provides the weak detectors allowed structure determination of single crystals linkage of these isolated Na octahedra and the mixed octa- down to about 0.05 mm, leading to comprehensive crystal- hedral tetrahedral framework. Raite is structurally related to chemical reviews (4–7). In the 1970s, the available x-ray intersilite, palygorskite, sepiolite, and amphibole. intensity began to increase dramatically as ‘‘synchrotron’’ radiation was extracted from bending magnets of synchronized Natural processes selected some 4,000 known mineral species accelerators originally designed for high-energy physics. New (Nomenclature Committee of the International Mineralogical generations of dedicated synchrotron sources are providing Association), of which several hundred have industrial appli- further advances in the intensity and particularly the quality cations. Most occur at the Earth’s surface. The crystal struc- [narrow angular divergence and energy spread; controlled tures of minerals are the key to understanding chemical and polarization; tunability from high (100 keV) to low energy]. physical processes on Earth, and for testing remote observa- The third-generation synchrotron x-ray sources are designed tions and ideas on the Solar System and Universe. Agriculture, around multi-magnet insertion devices (‘‘undulators’’ and the energy and metal industries, hydrology, and geobiology, in ‘‘wigglers’’). The European Synchrotron Research Facility particular, are based on chemical reactions in and on micro- (ESRF) in Grenoble, France (operational), the Advanced meter mineral grains. The petroleum and chemical industries Photon Source in Argonne, Illinois (commissioning), and the use zeolite catalysts (1), many of which are analogous with the Super Photon Ring-8 in Harima Science Garden City, Japan rare mineral faujasite. All advances in scientific technology (commissioning), permit various types of microanalysis (8), permit new science, and indeed should be driven thereby. including determination of the crystal structure of micrometer About one-fifth of known minerals lack a structure determi- single crystals, when beamlines are fully optimized by subtle nation,** mainly because crystals are too small or imperfect improvements in x-ray focusing, data collection, and computer for laboratory x-ray sources. This determination of the crystal processing. Second-generation synchrotron x-ray beams have structure of raite by using x-rays from a third-generation revolutionized the determination of a crystal structure from a synchrotron source opens the gate to a new field of micro- near-random powder of pure, well-crystallized material (9), geochemistry, which has important applications to agriculture, Abbreviation: ESRF, European Synchrotron Radiation Facility. † The publication costs of this article were defrayed in part by page charge To whom reprint requests should be addressed. e-mail: smith@ geo1.uchicago.edu. payment. This article must therefore be hereby marked ‘‘advertisement’’ in **See Crystal Structures of Minerals and Chemical Analogs, an unpub- accordance with 18 U.S.C. §1734 solely to indicate this fact. lished database updated weekly, compiled by J.V.S. at the University © 1997 by The National Academy of Sciences 0027-8424y97y9412263-5$2.00y0 of Chicago. Requests on specific minerals answered at smith@ PNAS is available online at http:yywww.pnas.org. geo1.uchicago.edu. 12263 Downloaded by guest on September 23, 2021 12264 Geology: Pluth et al. Proc. Natl. Acad. Sci. USA 94 (1997) but they lack the brilliance needed to determine the structure MATERIALS AND METHODS of a single crystal selected from the powder. Impure samples 3 of a poorly crystallized phase require single-crystal diffraction A single crystal with dimensions 3 3 3 3 65 mm , on a glass studies using third-generation synchrotron x-ray sources cou- fiber tapered to 1 mm, was mounted on a single-crystal pled with other techniques, including electron diffractiony k-geometry diffractometer at the ESRF (11). An x-ray beam microscopy and various spectroscopies. The third-generation from an undulator was focused to 30 mm by an ellipsoidal insertion devices provide x-ray beams intense enough for study mirror, and monochromatized to 0.6883 Å (18 keV) by a of single crystals somewhat smaller than 1 mm. channel-cut Si(111) crystal cooled by liquid nitrogen. Only half Current progress in recording diffraction data for small the volume or about 300 mm3 of the crystal was actually crystals is reviewed by Harding (10). Monochromatic data irradiated. Seventy-three frames were collected on a charged- recorded on a FAST ‘‘conventional’’ diffractometer has per- coupled area detector (11-cm fluorescent screen with lens mitted structure determination for crystals as small as 20–40 coupling) by rotating f 10° in 20 sec. mm, corresponding to crystal volume 3 scattering power of The DENZO program (14) yielded refined lattice constants of '5 3 1012 e2zÅ23. Usable synchrotron diffraction data have the monoclinic unit cell: a 5 15.1(1) Å; b 5 17.6(1) Å; c 5 been obtained from various crystals less than 1 mm3, including 5.290(4) Å; b 5 100.5(2)°; V 5 1382.33 Å3; space group C2ym. a study of thin plates of kaolinite at ESRF (11). SHELXTL (15) yielded solution and refinement of the crystal There are problems with the interpretation of diffuse dif- structure by using 6,599 reflections merged to 1,164 unique fraction streaks from small crystals such as the kaolinite plates. reflections: R(merge) 5 0.05; R 5 0.07. The final difference Such thin plates, and also narrow needles, may have insuffi- Fourier map was featureless: drmaximum and minimum were cient scatterers along the short directions. More complex and 0.98 eyÅ3 and 20.82 eyÅ3. Of the 3,080 reflections that should challenging is to evaluate diffuse scattering in terms of the be absent from C-centering, 325 were observed weakly above chemical and physical changes at the surface, where the atomic 1 s. Refinement in P2ym yielded essentially the same struc- environment must be different from the interior. Careful ture. Possible ordering of Ti in a weakly occupied site, or an control of the humidity will be neeeded for study of micro- intergrowth of raite with a second phase, needs further study. meter crystals that respond to hydrogen bonding. Even a Qualitative x-ray emission analysis of the needle with a microcrystal of diamond must have some type of termination Cameca SX-50 electron microprobe confirmed the major Mn, for the projecting electron orbitals, perhaps hydrogen or Na, Si, and minor Ti in the original three bulk chemical oxygen. analyses. Quantitative electron-probe analysis was ruled out by Hence a growing challenge for study of micrometer minerals decomposition in the electron beam.