Crystal Structures and Cation Sites of the Rock‐Forming Minerals Joseph R. Smyth Department of Geological Sciences, University of Colorado and David L. Bish Los Alamos National Laboratory Boston ALLEN & UNWIN 1 © J.R. Smyth and D.L. Bish, 1988 2 CONTENTS Acknowledgement Introduction Unit Cell Tables Systematic variation of site parameters Trace and minor element substitutions 1. Single Oxides 1.1. Cuprite group 1.2. Periclase group 1.3. Zincite group 1.4. Tenorite and montroydite 1.5. Corundum group 1.6. Bixbyite group 1.7. Arsenic and antimony sesquioxides 1.8. Rutile group 1.9. TiO2 polymorphs 1.10. MnO2 polymorphs 1.11. Uraninite 1.12. TeO2 polymorphs 2. Multiuple Oxides 2.1. Ilmenite Group 2.2. Perovskite group 2.3. Oxide spinel group 2.4. Pseudobrookite group 2.5. Tungstate group 3. Hydroxides 4. Orthosilicates 4.1. Garnet group 4.2. Olivine group 4.3. Silicate spinel group 4.4. Silicate zircon group 4.5. Willemite group 4.6. Aluminosilicate group 4.7. Humite group 4.8. Titanite group 3 4.9. Staurolite 5. Sorosilicates and cyclosilicates 5.1. Epidote group 5.2. Melilite group 5.3. Wadsleyite group 5.4. Lawsonite 5.5. Tourmaline group 5.6. Vesuvianite 6. Chain silicates 6.1. Orthopyroxenes and primitive clinopyroxenes 6.2. C‐centered clinopyroxenes 6.3. Pyroxenoids 6.4. Ortho‐amphiboles 6.5. Clino‐amphiboles 6.6. Aenigmatite 7. Layer silicates 7.1. Talc and pyrophyllite 7.2. Tri‐octahedral micas 7.3. Di‐octahedral micas 7.4. Clays 8. Framework silicates 8.1. Silica group 8.2. Alkali feldspar group 8.3. Alkaline earth feldspar group 8.4. Feldspathoid group 8.5. Beryl and cordierite 8.6. Scapolite group 8.7. Zeolite group 9. Carbonates, nitrates, sulfates and phosphates 9.1. Calcite group 9.2. Dolomite group 9.3. Aragonite group 9.4. Barite group 9.5. Gypsum and anhydrite 9.6. Apatite 9.7. Monazite 4 10. Halides 10.1. Halite group 10.2. Fluorite group 11. Cation sites listed by mean distance 11.1. Two‐ and three‐fold sites 11.2. Four‐fold sites 11.3. Five‐fold sites 11.4. Six‐fold sites 11.5. Seven‐fold sites 11.6. Eight‐fold sites 11.7. Sites of C.N. > 8 References Mineral index 5 Acknowledgement This work was supported in part by the U.S Department of Energy, Office of Basic Energy Sciences, through several grants to Los Alamos National Laboratory which is operated by the University of California under contract number W‐7405‐ENG‐6. The author s particularly thank Dr. George Kolstadt (OBES Chemistry, Earth and Life Sciences) and Dr. Ryszard Gajewski (OBES Advanced Energy Projects) for generous support of the project. The autyhords thank Drs. Y. Ohashi (ARCO, Plano, TX), R. X. Fischer (Johannes Gutenberg Universitaet, Mainz) and L.W. Finger (Carnegie Institution, Washington, DC) for providing computer codes and discussions, and Drs. George Zweig, Klaus Lackner, and Wes Myers (Los Alamos National Laboratory) for discussions, support and encouragement throughout the project. Theoretical Division Office of Los Alamos National Laboratory is also thanked for its support. Tamsin C. McCormick is gratefully acknowledged for tireless proofreading, technical assistanc and moral support. Preface to Online Edition This is the first installment of a free version of the first edition of the book. The data presented here are identical to those of the first edition and so should be cited as: Smyth, J.R. and D.L. Bish (1988) Crystal Structures and Cation Sites of the Rock‐Forming Minerals. Boston, Allen and Unwin, 332pp. 6 INTRODUCTION Over the past two decades, with the advent of automated x‐ray and neutron single‐crystal diffractometers, there has been a major improvement in the precision with which atom positions in minerals are known. Shannon and Prewitt (1969, 1970), Whittaker and Muntus (1970), and Shannon (1976) have compiled crystal structure data for synthetic compounds and minerals in order to estimate effective ionic radii. These compilations and estimates have proven immensely useful to geochemists, mineralogists, and petrologists in understanding the substitution behavior and distribution of elements in natural systems, eg. Onuma et al. (1968), Jensen (1973), Philpotts (1978). Whereas Bragg et al. (1965) and Zoltai and Stout (1984) have compiled descriptions of mineral structures, and Wyckoff (1963) has compiled atom location data for most inorganic structures, there has never been a compilation of data on the nature of cation sites in minerals. Robie et al. (1978) compiled thermodynamic data for many of the rock‐forming minerals and oxides. For some of these compounds there have been more recent and accurate cell determinations, so that improved data on molar volume and density are available. Further, thermodynamic data compilations do not include information on atomic environments in these compounds. We have undertaken a compilation of recent data on crystal structures for a large group of the common minerals. From atom positional and cell data, we have calculated nearest‐neighbor distances, coordination numbers, volumes of coordination polyhedra, distortion indices, and electrostatic energies in a consistent fashion. The objective in this work is to make the recent improvements in crystal structure data available to a larger group of petrologists and geochemists seeking to understand the chemical behavior of these minerals in natural systems. n order to reduce this to a manageable task we have had to make some rather arbitrary decisions in selecting and grouping the data. First, we have limited the group to the oxygen and halide minerals with the understanding that ionic radii have at least some relevance to these structures. This has led to the exclusion of the sulfides from the current compilation. In selecting structures, we have endeavored to choose ordered end‐members whenever possible so that cation site data will be more easily interpretable. In order to document atomic environments in standard thermodynamic states we have included a large number of simple oxide minerals. This has led to the inclusion of some less‐than‐ common minerals in this group, but otherwise we have included only the more common minerals of igneous, metamorphic, and sedimentary rocks. Finally, in order to facilitate comparisons, we have grouped together data from isomorphous structures, and in a few cases, polymorphous structures. This has led to a few instances of duplication which we feel are justified in order to allow comparisons. 7 Figure 0.1. Plot of angle variance versus quadratic elongation for SiO4 tetrahedra. Adjacent points are connected to show not only the strong correlation between the two factors, but but also that the angle variance occasionally falls below, but not above, the general trend (see text). Unit Cell Tables We have organized the structure data into those pertaining to unit cells and those pertaining to specific sites. In addition, we have summarized the site data, grouped them according to coordination number, and listed the cation sites by mean distance in Chapter 11. Within the mineral groups, unit cell tables consist of formula, formula weight, calculated density, molar volume, Z, crystal system, class, and space group, cell parameters, and reference. In general, the formula is that given in the reference, except that we have omitted elements constituting less than 1.0 weight percent of the mineral. In a few 8 instances we have recalculated formulas to the same number of oxygen atoms for comparison across an isomorphous series. The formula weight, density, and molar volume are our calculation from the stated formula and unit cell volume. Z is the number of formula units per cell. The reference is not repeated in the site tables, but site data are presented sequentially in the same order permitting unambiguous citation. Site Data Tables Similar sites in isomorphous series are grouped together to facilitate comparisons and show variability of analogous features across the series. The tabulated data consist of a site name, coordination number (C.N.), occupants, point symmetry, Wyckoff notation, cation fractional coordinates, nearest neighbor distances, mean and standard deviation of distances, polyhedral volume, quadratic elongation, variance of central angle, electrostatic site energy, and a model charge. The coordination number is the number of nearest anion neighbors. The occupant is that inferred from the formula or stated in the reference. In a few instances, for partially occupied sites, a total site occupancy is given. Tetrahedral Al‐Si occupancies for some of the zeolites were calculated from the mean T‐0 distance when site occupancies were not reported. The point symmetry and Wyckoff notation are those for the site (Hahn, 1983). Fractional coordinates for the site are included to avoid any ambiguities in site nomenclature that may arise and to show variability across the series. Individual nearest neighbor distances are given throughout with a major exception being those for the framework silicate structures (Chapter 8). With the low symmetries of many of these structures, it was found very difficult to present these in a way that would be both concise and meaningful. Also, we have omitted the cavity geometries for the zeolites as these are documented elsewhere (Mortier, 1982). The mean distance is our calculated average of the given distances. The is the standard deviation of the distances. It is thus an estimate of the distortion of the site, not an estimate of the error in the determination. Errors are regrettably not given because this would have more than doubled the size of the data base, greatly complicating the handling of the data. The polyhedral volume (Poly. Vol.), quadratic elongation (Q.E.), and angle variance (Ang.Var.) were calculated with a slightly modified version of the program VOLCAL (L.W. Finger, personal communication). The units of polyhedral volume are cubic Angstroms. Quadratic elongation as defined by Robinson et al.