STRUCTURAL VARIATION in the PHOSPHATE OLIVINE LITHIOPHILITE- TRIPHYLITE SERIES and CHARACTERIZATION of LIGHT ELEMENT (Li, Be, AN

Home , Glaucochroite, Hambergite, Lithiophilite, Natrophilite, Spodumene

STRUCTURAL VARIATION IN THE PHOSPHATE OLIVINE LITHIOPHILITE-

TRIPHYLITE SERIES AND CHARACTERIZATION OF LIGHT ELEMENT (Li, Be,

AND B) MINERAL STANDARDS

Arthur Bill Losey

Abstract

This research is comprised of two projects involving the use of single crystal X- ray diffraction to for mineral structure determination. Chapter 1 involves determination of structural variation along the Mn ⇔ Fe solid solution of the lithiophilite-triphylite series, olivine structure types. Bond lengths and angle variance are examined to determine their variation along the Mn ⇔ Fe join and their relationships to other silicate and germanate olivine structures. The angle variance of the phosphate olivines was smaller in the M1 octahedron, which is in contrast to the other olivine structure phases examined in this study.

In Chapter 2, diffraction data were collected on phenakite, danburite, spodumene, hambergite, lithiophilite, axinite, and prismatine, which are to be used as light element

(Li, Be, and B) mineral standards. The data were used to determine the atomic positional parameters, site geometry, site occupancy, and polyhedral connectivity of each sample. STRUCTURAL VARIATION IN THE PHOSPHATE OLIVINE LITHIOPHILITE-

TRIPHYLITE SERIES AND CHARACTERIZATION OF LIGHT ELEMENT (Li, Be,

AND B) MINERAL STANDARDS

A Thesis

Submitted to the

Faculty of Miami University

In partial fulfillment of

The requirements for the degree of

Master of Science

Department of Geology

Arthur Bill Losey

Miami University

Oxford, Ohio

2001

Advisor Dr. John F. Rakovan

Reader Dr. John M. Hughes TABLE OF CONTENTS

Page

Chapter 1 1

Structural Variation in the Phosphate Olivine Lithiophilite-Triphylite Series

Chapter 2 27

Structure Refinement of Light Element (Li, Be and B) Mineral Standards

ii TABLES

Page

Chapter 1 - Tables (1-4) 17

Table 1. Electron-microprobe results for the lithiophilite-triphylite 17

Series samples.

Table 2. Crystal data and results of structure refinements for 18

lithiophilite-triphylite series samples.

Table 3. Positional parameters and isotropic B values for atoms 19

in the lithiophilite-triphylite series samples.

Table 4. Bond length (Å) and tetrahedral bond angles (°) for 20

the lithiophilite-triphylite series samples.

Chapter 2 - Tables (1-8) 39

Table 1. Crystal data and structure refinement results. 39

Table 2. Atomic positional parameters and isotropic B values 40

for phenakite.

Table 3. Atomic positional parameters and isotropic B values 41

for danburite.

Table 4. Atomic positional parameters and isotropic B values 42

for spodumene.

Table 5. Atomic positional parameters and isotropic B values 43

for hambergite.

Table 6. Atomic positional parameters and isotropic B values 44

for lithiophilite.

iii Table 7. Atomic positional parameters and isotropic B values 45

for axinite.

Table 8. Atomic positional parameters and isotropic B values 46

for prismatine.

iv TABLE OF FIGURES

Page

Chapter 1 - Figures (1-6) 21

Figure 1. (001) projection of the lithiophilite-triphylite series crystal 21

structure.

Figure 2. Composition versus the bond lengths of the M2 site. 22

Figure 3. Composition versus the bond lengths of the M1 site. 23

Figure 4. O3 site geometry and the bond length variation that occurs 24

with Fe substitution for Mn.

Figure 5. Variation in the M1 and M2 angle variance across the 25

lithiophilite-triphylite series samples..

Figure 6. (a) T angle variance versus T cation radius. (b) M1/M2 26

angle variance versus T cation radius.

v Acknowledgements

I would first like to thank my advisor John Rakovan for all of your guidance and support over my graduate career. Even though the apatite project was not feasible at this time, you were very supportive in suggesting alternate projects to research. John Hughes was also instrumental in the development and understanding of these single crystal X-ray diffraction studies. I would also like to thank you both for you patience, sharing your vast knowledge, and making my time at Miami University both challenging and enjoyable. I would like to add a special thanks to John Hughes for his understanding with the flow-through switch fiasco.

I would also like to thank Darby Dyar and Carl Francis. Both contributed samples and chemical analyses that were used in these studies. I would also like to thank them for their comments and discussions about this research.

Bill Lack of the Instrumentation Lab was also essential to my research. He kept the Cad4 in working condition and was always there on a moments notice to make repairs whenever they were necessary.

I would like to thank all of the graduate students for their support and their discussions about crystallography. Even though this may not have been your area of expertise, talking with others was very helpful to my understanding of these projects. I would also like to especially thank Darin, C.B., Matt, and Shawn for their help with computing problems and for our lunchtime trips uptown.

Special thanks goes to Kathleen Counter Benison. If it wasn’t for your help and encouragement during my undergraduate education, I would not have made it this far in the first place.

vi Finally, thanks to everyone who turned a blind eye to my best friends T.J. and

Otter. Their presence always brightened my day and made those tough and stressful days a little easier.

vii CHAPTER 1

STRUCTURAL VARIATION IN THE PHOSPHATE OLIVINE LITHIOPHILITE-

TRIPHYLITE SERIES

Submitted to Canadian Mineralogist

1 ABSTRACT

The crystal structures of five natural lithiophilite-triphylite series [Li(Mn,Fe)PO4] samples were refined to determine structural variation along the Mn ⇔ Fe solid solution and to elucidate variations in the Pnma olivine atomic arrangement. The refinements converged to R ≤ 0.017. Bonds at the O3 site are fundamental in understanding the response of the atomic arrangement as Fe concentration increases. The M2-O3a bond shortens by more than 0.06 Å and the M2-O3b bond shortens by ~ 0.02 Å over the solid solution series. This shift of the O3 oxygen toward the two coordinating M2 sites causes the M1-O3 bond to increase by approximately 0.03 Å, thus causing significant structural changes in the M1 site. Much previous work has focused on polyhedral distortions in the olivine structure. The angle variance for the M1, M2, and T polyhedra were calculated for each phosphate sample and published silicate and germanate olivine structures. In each case, the angle variance of the phosphate olivines was smaller in the M1 octahedron, which is in contrast to the other olivine structure phases examined in this study.

However, examination of numerous olivine structures demonstrate that if the size difference in the radius of the M1 and M2 site cation is ≥ 0.17 Å the distortion is greater in the octahedral site that is occupied by the larger cation.

Keywords: lithiophilite, triphylite, olivine structure, crystal structure.

SOMMAIRE

2 Mots-clés:

INTRODUCTION

Minerals of the lithiophilite-triphylite series [Li(Mn,Fe)PO4] occur in evolved

granitic pegmatites that are enriched in both Li and P. These phases are isostructural with

olivine (Fig. 1). The octahedral cations in the lithiophilite-triphylite series are completely

ordered between the M1 and M2 sites. Li only occupies the M1 site, whereas the M2 site

is occupied by divalent Mn, Fe, and in some cases Mg. This complete ordering of cations

is in contrast to the majority of olivine-structure phases in which there is extensive

disordering of octahedral cations.

Natrophilite (NaMnPO4) is also completely ordered, and is the only ordered

olivine structure where the M1 cation is much larger than the divalent M2 cation (Moore

1972). In other ordered olivines such as monticellite (MgCaSiO4) and glaucochroite

(MnCaSiO4), the divalent cations in the M1 site are smaller than the cations in the M2 site (Lager & Meagher 1978).

Olivine is one of the most important upper mantle silicate phases. Various olivine group minerals occur in rocks with very diverse geochemical histories (Brown 1980), attesting to the importance of understanding the olivine atomic arrangement.

Understanding cation ordering in the olivine structure has given insights into cation partitioning between melts and coexisting mineral phases (Brown 1980).

Little structure work has been performed on members of the lithiophilite-triphylite series, particularly with respect to structural variations that occur with the Mn ⇔ Fe solid

3 solution. In many of the previous single crystal X-ray studies of these phases, synthetic samples were used (Yakubovich et al. 1977; Streltsov et. al. 1993; Geller & Durand

1960). Structure refinements using natural samples were performed by Finger & Rapp

(1969).

There have also been studies on the relationship between composition and unit cell parameters (Lumpkin & Ribbe 1983; Fransolet et al. 1984) in the lithiophilite- triphylite series. Fransolet et al. (1984) attempted to determine the Mn/(Mn+Fe) ratio from powder diffraction experiments. However, those methods were not found to accurately predict the unit cell parameters or Mn/(Mn+Fe) divalent cation ratios of our samples. Lumpkin & Ribbe (1983) and Fransolet et al. (1984) did note a structural variation with composition.

In this study, single crystal X-ray diffraction experiments were performed on natural lithiophilite-triphylite samples with Mn/(Mn+Fe) ratios of 94, 73, 50, 21, and 11

(referred to as Lth94, etc.). The atomic arrangement of each sample was refined to elucidate the structural changes with composition in this series. Structural information for the Fe end member, Lth0, used for comparisons in this paper was taken from Streltsov et al. (1993).

EXPERIMENTAL DETAILS

Microprobe analysis

4 Compositional analyses of the lithiophilite-triphylite samples (Lth94, Lth50,

Lth21, and Lth11) were performed on a Cameca MBX electron microprobe using WDS

in the Department of Earth and Planetary Sciences at Harvard University (Table 1).

Beam conditions were: 15 KeV, 23 nA, 16 x 16 µm raster. Sandia BA85 was used for

matrix corrections assuming 9.5 wt.% Li2O. K-alpha lines were used for all elements.

Standards used were albite (Na), enstatite (Mg, Si), apatite (P, Ca), tephroite (Mn), and

fayalite (Fe). Lth73 was analyzed by Dyar et al. (Table 1; in press).

Data collection

Single crystals of the five lithiophilite-triphylite samples were isolated and ground

to 150-200 µm ellipsoids. Each sample was then mounted on an Enraf-Nonius CAD-4

diffractometer utilizing graphite-monochromatized MoKα X-radiation for data collection

of a hemisphere of reciprocal space. Cell parameters (Table 2) were calculated by least-

squares refinement of the setting angles of twenty-five automatically centered reflections,

each measured in four positions. Crystal data and refinements details are found in Table

Structure Refinements

The SDP for Windows package of programs (Frenz 1997) was used to refine the atomic arrangement, using a starting lithiophilite-triphylite model (Streltsov et al. 1993),

I > 3σΙ data, and neutral-atom scattering factors with terms for anomalous dispersion.

5 Absorption was corrected using 360° ψ-scan data for three reflections and their Friedel

equivalents. A weighting scheme with weights proportional to σ -2 and a term to

downweigh intense reflections was used throughout the refinement. In the refinements,

Li, P, and O1-O3 were fixed to fully occupy their respective sites. The M1 site was

modeled with Li and the M2 site was modeled with Mn (Lth94, Lth73, and Lth50) or Fe

(Lth21 and Lth11).

The atomic arrangements of the five samples refined routinely. Each of the

refinements converged to R ~ 0.017 (Table 2). The release of the Mn/Fe site had no

significant affect on the structure refinement due to the similar scattering factors of Mn

and Fe, with the exception of the Lth11 sample. This sample would only refine to R ~

0.032 before the release of the M2 site occupancy. The refinement improved to R ~

0.017 after the release of the Fe site due to the significant amount of Mg (0.23 apfu) in

this sample.

The atomic parameters are found in Table 3 and the bond lengths and tetrahedral

angles are listed in Table 4 (anisotropic thermal parameters and structure factors may be

obtained from the Depository of Unpublished Data, CISTI, National Research Council Of

Canada, Ottawa, Ontario K1A 0S2).

RESULTS AND DISCUSSION

Structural variations with composition

6 The substitution of Fe2+ (r = 0.78 Å; Shannon 1976) for Mn2+ (r = 0.83 Å;

Shannon 1976) in the lithiophilite-triphylite series suggests that a concomitant shortening

of the octahedral bond lengths with oxygen should occur. Figure 2 confirms that

observation, depicting the variation of M2-O bond lengths with composition along the

Mn ⇔ Fe join. Note that sample Lth11, which contains substantial amounts of Mg, often

lies off the variation trend of the other samples, indicating that incorporation of the

smaller Mg ion (r = 0.72 Å; Shannon 1976) affects the variation in the octahedral bond

length to a greater extent.

Although the shortening of the M2 octahedral bond lengths are expected, the bond

length variations in that polyhedron also induce bond length variations in the M1

polyhedron, occupied solely by Li. Figure 3 depicts the variations of the M1-O bond

lengths. The M1-O1 and M1-O2 bond lengths decrease, whereas the M1-O3 bond length

increases with increasing Fe substitution. This occurs with no substitutions of cations for

Li in the M1 site.

The variations in bond lengths of the M1 and M2 sites along the Mn ⇔ Fe solid solution are not equivalent to the three oxygen atoms. The M1 site is octahedrally coordinated and consists of two symmetrically-equivalent bonds to each of the three oxygen ligands. The M2 site is also octahedrally coordinated. However, the M2 site has one bond to the O1 and O2 sites and four bonds to O3 site, with two different lengths

(referred to as O3a and O3b). Figure 2a-e and Figure 3a-d demonstrate the relationship between Fe composition and the cation-oxygen bond lengths. The changes in the M1 and

M2 site bond lengths are dependent on the composition of the M2 site. However, the changes in the bond lengths that occur with the increase in Fe concentration is influenced

7 by O3 site coordination. We here examine structural changes that occur with respect to

O3.

O3 Site

The O3 oxygen is unique among the anion sites in the olivine structure, and is

important in understanding the response of the atomic arrangement to the Mn ⇔ Fe substitution at the M2 site in the lithiophilite-triphylite series. The O3 oxygen is the only anion that bonds to two M2 sites; O1 and O2 bond to only one M2 site.

The largest bond-length variation with cation substitution in the series is in the

M2-O3a bond (Table 4), which shortens by more than 0.06 Å (Fig. 2c) with substitution of Fe over the range of Mn ⇔ Fe studied. The M2-O3b bond contracts by ~ 0.02 Å (Fig.

2d) over the same range of solid solution. Figure 4 characterizes the coordination of O3 and depicts the changes that occur as Fe substitutes for Mn in the M2 site.

In addition to bonding to two M2 ions, O3 also bonds to one M1 site. Because of the shift of the O3 oxygen toward the two coordinating M2 sites, the bond to M1 increases by approximately 0.03Å with substitution of the smaller Fe atom in M2 site; thus, the shortening of the M2-O3 bonds induces a lengthening of the M1-O3 bonds (Fig.

3c). The loss of bond valence at the M1 site from the lengthened M1-O3 bond is more than compensated by shortening of other M1-O bonds (Fig. 3a; Fig. 3b).

Octahedral distortion

8 Composition varies greatly among phases with the olivine structure, but the M1 and M2 octahedra are distorted regardless of the site occupant (Brown 1980; Fleet 1974).

There is a large difference between the geometries of the M1 and M2 octahedra. The M1 octahedron shares six edges with other polyhedra, two each with M1, M2, and T polyhedra.

The M2 octahedral distortion is much more complex. The M2 occupant is not centered in the M2 octahedron, as is the cation of the M1 octahedron. This is a response to cation repulsions across the three shared polyhedra edges, two with M1 polyhedra and one with a tetrahedron (Brown 1980; Fleet 1974). The M2-T repulsive force has the greatest affect on the M2 octahedral bond lengths (Brown 1980). This is especially apparent in the M2-O3 bond lengths and is illustrated in Table 4. The O3b oxygen atom is on the edge shared between the M2-T polyhedra. The cation repulsion across the M2-

T edge causes the M2-O3b bond to lengthen and concomitantly the opposite M2-O3a bond to shorten to compensate for this cation repulsion.

The angle variance, defined by Robinson et al. (1971), was used to quantify the octahedral and tetrahedral distortion in our samples and other olivines. Robinson et al.

(1971) concluded that the M1 octahedron is more distorted than the M2 octahedron and that angle variance increases as cation size increases in olivine group minerals. This holds true for the angle variance of many olivine type structures, such as fayalite (Smyth

1975), forsterite (Smyth & Hazen 1973), Ni-olivine (Lager & Meagher 1978), and natrophilite (Moore 1972).

Conversely, in the lithiophilite-triphylite series, the M1 octahedral angle variance is lower than the M2 octahedron in every sample. The angle variance of the end

9 members of the Mn ⇔ Fe solid solution are 144.354(3)°2 and 152.153(2)°2 (M1 and M2

octahedra respectively) for Lth94 and the angle variance for Lth0 is 150.8°2 and 154.1°2

(M1 and M2 octahedra respectively; Fig. 5).

The angle variance of the T site in the olivine structure varies greatly with the T site occupant. The T site shares three edges, one with M2 and two with M1; the O-T-O angle of the shared edges contribute 45-80% of the total tetrahedral angle variance in phosphate, silicate, and germanate olivines. Figure 6a shows the relationship of tetrahedral cation size to the tetrahedral angle variance for phosphate, silicate, and germanate olivines. Figure 6a demonstrates that although there is considerable variation in the tetrahedral angle variance among olivine structures with the same tetrahedral occupant, the tetrahedral angle variance increases with increasing tetrahedral cation radius. The relatively large angle variance among structures with the same tetrahedral cation suggests that the T site in the olivine structure is not static and is affected by interactions with connecting polyhedra.

The edge shared between the M1 and T sites along O2-O3 has the greatest effect on the M1 angle variance. Approximately 45% of the angle variance of the M1 site results from the two O2-M1-O3 angles. In silicate olivines the O2-T-O3 is also the most distorted tetrahedral angle. The shared edge with the M2 octahedron along O1-O3 only has a minor contribution to the overall M1 angle variance.

The O3a-M2-O3a and O3b-M2-O3b angles account for ~ 75% to 85% of the olivine M2 angle variance. The M2 octahedron shares one edge with the T site along

O3b-O3b and in phosphate and germanate olivines this is the most distorted of the O-T-O angles. However, the O3a-M2-O3a angle is also indirectly influenced by the T site. The

10 O3a and O3b positions in the M2 site are determined by the center of symmetry at the

M1 site. Thus as the O3b atoms of the M2 site move closer together along the M2-T shared edge the O3a atoms mover further apart.

Figure 6b displays the M1/M2 angle variance versus the tetrahedral cation size.

Note that the smaller the tetrahedral cation the lower the M1/M2 angle variance ratio. In these examples, the phosphates exhibit an angle variance wherein M1 < M2. The converse is true for the silicate and germanate olivines. However, there are exceptions in the phosphate and silicate olivines where the angle variance is larger in M1 for phosphate olivines and larger in M2 for silicate olivines. However, in these phosphate and silicate olivines there is a large size difference between the M1 and M2 cation radius (≥ 0.17 Å).

The large cation size difference in natrophilite (NaMnPO4; Moore 1972), monticellite

(MgCaSiO4), and glaucochroite (MnCaSiO4; Lager & Meagher 1978) is ≥ 0.17 Å. In these olivine structures, the site that is occupied by the larger cation exhibits the larger octahedral angle variance.

SUMMARY

The bond length variations in both the M1 and M2 sites of the lithiophilite- triphylite series are correlated to the composition of the M2 site. The M1 and M2 site bond lengths decrease as the concentration of Fe increases, with the exception of M1-O3 bond. In addition, the angle variance in the lithiophilite-triphylite series does not show the same trend as in many other olivine structure types. In each case, the angle variance of the phosphate olivines was smaller in the M1 octahedron, which is in contrast to the

11 other olivine structure phases examined in this study. However, exanimation of numerous olivine structures demonstrate that if the size difference in the radius of the M1 and M2 site cation is ≥ 0.17 Å the distortion is greater in the octahedral site that is occupied by the larger cation.

12 REFERENCES

BELOKONEVA, E.L., BELOV, N.V., IVANOV, Y. A. & SIMONOV, M.A. (1972): Crystal

structure of cadmium orthogermanate Cd2GeO4. Sov. Phys. Crystallogr. 17, 177-

179.

BROWN, G.E. (1980): Olivine and silicate spinels. In Orthosilicates (P.H. Ribbe ed.). Rev.

Mineral. 5, 275-381.

& PREWITT, C.T. (1973): High-Temperature Crystal Chemistry of Hortonolite.

Am. Mineral. 58, 577-587.

DUDKA, A.P., KAMINSKII, A.A. & SIMONOV, V.I. (1986): Refinement of NaGdGeO4,

NaYGeO4, and NaLuGeO4 single-crystal structures. Physica Status Solidi. A93,

495-502.

DYAR, M.D., WIEDENBECK, M., ROBERTSON, D., CROSS, L.R., DELANEY, J.S.,

FERGUSON, K., FRANCIS, C.A., GREW, E.S., GUIDOTTI, C.V., HERVIG, R.L.,

HUGHES, J.M., HUSLER, J., LEEMAN, W., MCGUIRE, A.V., RHEDE, D., ROTHE, H.,

PAUL, R.L., RICHARDS, I. & YATES, M. (in press): Reference minerals for the

microanalysis of light elements. Geostand. Newslett. 25.

FINGER, L.W. & RAPP, G.R. (1969): Refinement of the crystal structure of triphylite.

Carnegie Inst. Wash. Year book. 68, 290-292.

FLEET, M.E. (1974): Distortions in the coordination polyhedra of M site atoms in

olivines, clinopyroxenes, and amphiboles. Am. Mineral. 59, 1083-1093.

13 FRANSOLET, A.M., ANTENUCCI, D., SPEETJENS, J.M. & TARTE, P. (1984): An X-ray

determinative method for the divalent cation ratio in the triphylite-lithiophilite

series. Mineral. Mag. 48, 373-381.

FRENZ, B.A. (1997): SDP for Windows Reference Manual. B.A. Frenz and Associates,

Inc., College Station, Texas.

GELLER, S. & DURAND, J.L. (1960): Refinement of the structure LiMnPO4. Acta

Crystallogr. 13, 325-331.

HAZEN, R.M. (1987): High-pressure crystal chemistry of chrysoberyl, Al2BeO4; insights

on the origin of olivine elastic anisotropy. Phys. Chem. Mineral. 14, 13-20.

KIMATA, M. & NISHIDA, N. (1987): The crystal structure of Co-monticellite Ca1.255

Co0.745SiO4 and its significance as a solid solution crystal. Neues. Jb. Miner.

Monat. 1987, 160-170.

KUDOH Y. & TAKEDA H. (1986): Single crystal X-ray diffraction sudy on the bond

compressibility of fayalite. Physica. 139, 333-336.

LAGER, G.A. & MEAGHER, E.P. (1978): High-temperature structural study of six olivines.

Am. Mineral. 63, 365-377.

LUMPKIN, G.R. & RIBBE, P.H. (1983): Composition, order-disorder and lattice

parameters of olivines: relationships in silicate, germanate, beryllate, phosphate

and borate olivines. Am. Mineral. 68, 164-176.

MIYAKE M., NAKAMURA H. &KOJIMA H. (1987): Cation ordering in Co-Mg olivine

solid-solution series. Am. Mineral. 72, 594-598.

MOORE, P.B. (1972): Natrophilite, NaMn(PO4), has ordered cations. Am. Mineral. 57,

1333-1344.

14 MORIMOTO, N., KOTO, K., TOKONAMI, M. & WATANABE, M. (1974): Crystal Structures

of Three Polymorphs of Co2SiO4. Am. Mineral. 59, 475-485.

MOTOYAMA, T. & MATSUMOTO, T. (1989): The crystal structures and the cation

distributions of Mg and Fe of natural olivines. Mineral. J. 14, 338-350.

RAJAMANI, V., BROWN, G.E. & PREWITT, C.T. (1975): Cation ordering in Ni-Mg olivine.

Am. Mineral. 60, 292-299.

ROBINSON, K., GIBBS, G.V. & RIBBE, P.H. (1971): Quadratic elongation: a quantitative

measure of distortion in coordination polyhedra. Sci. 172, 567-570.

SHANNON, R.D. (1976): Revised effective ionic radii and systematic studies of

interatomic distances in halides and chalcogenides. Acta Crystallogr. A32, 751-

767.

SMYTH, J.R. (1975): High temperature crystal chemistry of fayalite. Am. Mineral. 60,

1092-1097.

& HAZEN, R.M. (1973): The crystal structures of forsterite and hortonolite at

several temperatures up to 900 C. Am. Mineral. 58, 588-593.

STRELTSOV, V.A., BELOKONEVA, E.L., TSIRELSON,V.G. & HANSEN, N.K. (1993):

Multipole analysis of the electron density in triphylite, LiFePO4, using X-ray

diffraction data. Acta. Crystallogr. B49, 147-153.

TAKEUCHI, Y., HAGA, N., HIRANO, M. & YAMANAKA, T. (1984): High-temperature

structural study of olivine-type structures and spinels. Mater. Sci. Earth’s

interior. 191-231.

TOUBOL, M. & TOLEDANO, P. (1987) Structure du germanate d’indium et de lithium.

Acta. Crystallogr. C43, 2004-2006.

15 WILL, G., BELLOTTO, M., PARRISH, W. & HART, M. (1988): Crystal structures of quartz

and magnesium germanate by profile analysis of synchrotron-radiation high-

resolution powder data. J. Apl. Cryst. 21, 182-191.

YAKUBOVICH, O.V., SIMONOV, M.A. & BELOV, N.V. (1977): The crystal structure of a

synthetic triphylite LiFe[PO4]. Sov. Phys. Dokl. 22, 347-350.

17 18

20 21

26 CHAPTER 2

Structure Refinement of Light Element (Li, Be and B) Mineral Standards

Submitted to Geostandards Newsletter: The Journal of Geostandards and Geoanalysis

27 Abstract

This is a continuation of the work of Dyar et al. (in press) to further characterize light element (Li, Be and B) mineral standards. Single crystal X-ray diffraction data were collected from phenakite, danburite, spodumene, hambergite, lithiophilite, axinite and prismatine. These data were used to refine the atomic positional parameters of each of the listed mineral standards. Each structure refinement converged to R ≤ 0.028. These data were also used to determine cation substitutions, site occupancy and polyhedral connectivity. Light elements are very important in geologic systems. They give insight into charge balance, cation exchange equilbria and are used as thermodynamic fluid tracers. Also, techniques such as SIMS, require well characterized homogeneous referance materials that are closely matched to the materials in question, both chemically and structurally. Thus, structurally characterizing and quantifying precise abundances of light elements in rocks and minerals has gained more attention in recent years.

28 Introduction

The importance of light elements in geologic systems has become more apparent in recent years. The abundance of these elements in various minerals is important in understanding the charge balance, stoichiometry and cation exchange equilbria in minerals and rocks. Light elements are also important fluid tracers and are crucial in understanding thermodynamic processes of minerals in which these elements are major constituents. However, quantifying precise concentrations of these elements in minerals has proven to be very difficult.

Varying analytical techniques yield very different amounts of light elements in the same samples. A round-robin study of the chemistry of tourmaline shows this lack of agreement for light elements (Dyar et al. 1998). Such discrepancies were also shown in various analyses of other B and Li rich minerals (Grew et al. 1990). This has prompted the characterization of Li, Be and B minerals by multiple techniques in order to find a set of analytical standards for these light elements.

Contrasting results can make it very difficult to determine which technique yields accurate concentrations for these elements. A set of standards will make calibration for light elements possible for most analytical techniques. In order to accomplish this task, as much information as possible must be known about these standards to fully trust the homogeneity and the given concentrations of light elements in these samples. Dyar et al.

(in press) has compiled and quantified precise measurements of light elements in a suit of minerals to be used as standards for Li, Be and B.

Single crystal X-ray diffraction experiments were preformed to determine the atomic arrangement of the following standards: phenakite, danburite, spodumene,

29 hambergite, lithiophilite, axinite, and prismatine. Site geometry, occupancy and polyhedral connectivity are reported to increase the understanding of the crystal chemistry of these standards. The importance of the structural characterization of these reference materials cannot be understated. SIMS, one of the major analytical tools, is dependant on reference materials that are compositionally and structurally similar to the material in question.

Experimental Details

Samples of phenakite, danburite, spodumene, hambergite, lithiophilite, axinite and prismatine were obtained from the Harvard Mineralogical Museum. Sample catalog numbers are listed under the specimen names in Table 1. Chemical analysis, by multiple techniques, of each sample can be found in Dyar et al. (in press).

Data collection

Single crystals of phenakite, danburite, spodumene, hambergite, lithiophilite and axinite were isolated and ground to 120-200 µm ellipsoids. Each sample, except axinite,

(crystal data and structural details are found in Table 1) was then mounted on an Enraf-

Nonius CAD-4 diffractometer utilizing graphite-monochromatized MoKα X-radiation for data collection of a hemisphere of reciprocal space. Cell parameters (Table 1) were calculated by least-squares refinement of the setting angles of twenty-five automatically centered reflections, each measured in four positions, for each sample. The parameters used to collect the intensity data are found in Table 1.

30 The axinite sample was mounted on a Bruker Apex CCD diffractometer equipped

with MoKα X-radiation for data collection of a sphere of reciprocal space. Refined cell-

parameters (7963 reflections) and other crystal data are listed in Table 1. Data were

collected and corrected for Lorentz and polarization factors using the Bruker program

Saint.

Structure Refinements

The SDP for Windows package of programs (Frenz 1997) was used to refine the atomic arrangement of phenakite, danburite, spodumene, hambergite and lithiophilite using starting models from previously published structures, I > 3σΙ data, and neutral-atom

scattering factors with terms for anomalous dispersion. Absorption was corrected using

360° ψ-scan data for three reflections and their Friedel equivalents. A weighting scheme

with weights proportional to σ -2 and a term to downweigh intense reflections was used

throughout the refinement.

The structure of axinite was refined by least-squares refinement utilizing the

programs in the Bruker Shelxtl V. 6.10 package of programs, with neutral-atom

scattering factors and terms for anolomous dispersion. The refinement was also

undertaken with anisotropic thermal parameters for all non-hydrogen atoms.

Results

31 Phenakite

The structure of phenakite (Be2SiO4) was refined using a starting model from

Downs and Gibbs (1987). The atomic arrangement of phenakite refined routinely and the refinement converged to R ~ 0.028. The atomic positions are listed in Table 2. The phenakite structure consists of three tetrahedral cation sites. Be occupies two distinctly different tetrahedral sites while Si occupies the remaining tetrahedral site. Each of the Be tetrahedron are connected to the other two tetrahedra by corner sharing at each O site.

Danburite

The structure of danburite (CaB2Si2O8) was refined using a starting model of

Phillips et al. (1974). The atomic arrangement of danburite refined routinely and the refinement converged to R ~ 0.018. The atomic positions are listed in Table 3. The danburite structure is comprised of Ca in 7-fold coordination and B and Si in tetrahedral coordination. The B tetrahedron shares one edge with the Ca polyhedra along O1-O2, there is also corner sharing with Si tetrahedra at each of these oxygen sites. The remaining corners in the B tetrahedron, O3 and O5 are shared with another B tetrahedron and Ca polyhedron respectively.

Spodumene

32 The structure of spodumene (LiAlSi2O6) was refined using a starting model of

Cameron et al. (1973). The atomic arrangement of spodumene refined routinely and the

refinement converged to R ~ 0.018. The atomic positions are listed in Table 4. The

spodumene structure consists of two symmetrically non-equivalent octahedral sites (Li

and Al) and Si in a tetrahedral site. The Li octahedron shares three edges with other

polyhedra, two edges are shared with Al octahedra along O1-O1 and O1-O2, and one

edge is shared with a Si tetrahedron along O2-O3. There is also corner sharing with Si at

the O1 and O3 sites.

Hambergite (102984)

The structure of hambergite [Be2(BO3)(OH)] was refined using a starting model of Burns et al. (1995). The atomic arrangement of hambergite refined routinely and the refinement converged to R ~ 0.024. The atomic positions are listed in Table 5. The structure consists of two symmetrically non-equivalent Be tetrahedral sites and a B trigional planer site. The Be tetrahedron share corners with other Be tetrahedron and B triangles. The Be tetrahedron also bond to an OH group (Burns et al. 1995) at the O4 site.

Lithiophilite (12944)

The structure of lithiophilite [Li(Mn,Fe)PO4] was refined using a starting model

of Streltsov et al. (1993). The atomic arrangement of lithiophilite refined routinely and

33 the refinement converged to R ~ 0.017. The atomic positions are listed in Table 6. The

structure has a P tetrahedral site and two octahedral sites M1 and M2. The M1 occupant

is Li whereas the M2 occupant is mainly Mn and Fe. However, Mg can also substitute in

the M2 site (Losey et al. submitted). The Li (M1) octahedron shares 6 edges with other

polyhedra, two shared edges are with other M1 octahedron along O1-O2, 2 edges with

M2 octahedra along O1-O3 and two edges with the P tetrahedra also along O2-O3. The

M1 octahedron also shared corners with the M2 octahedra at the O2 site and at two of the

four O3 sites.

Axinite (133711)

The structure of axinite [Ca2Al2(Fe,Mg,Mn)BSi4O15(OH)] was refined using the

starting model of Swinnea et al. (1981). The refinement converged to R ~ 0.023. The

atomic positions are listed in Table 7. In the axinite structure, B and Si are in tetrahedral

coordination and the remaining cations are only found in octahedral coordination. The

site refinements revealed that the 2+ cations substitute in the Fe site. This was also observed by Swinnea et al. (1981). The B tetrahedra shares two edges, one shared edge is along O3-O6 with the Ca octahedron and the other shared edge is along O6-O8 with the Fe octahedron. The B tetrahedron shares corners with Si tetrahedron at the O3, O6 and O8 sites. There is also corner sharing with two Al octahedra and a Ca octahedron at the O15 site.

34 Prismatine (112233)

The structure of prismatine [(Mg, Fe, )(Al,Mg,Fe)9(Si,Al)(B,Si,Al)O21(OH)] was refined using the starting model of Klaska and Grew (1991). The refinement converged to R ~ 0.023 and the atomic positions are listed in Table 8. The prismatine structure contains three different cation coordinations; cubic (Fe and Mg), octahedral (Al,

Mg, and Fe) and tetrahedral (Al, B, and Si). The B3 site, in this sample, is nearly fully occupied by B. The B tetrahedron shares a corner with two Al5 octahedra and the Mg1 octahedron at the O8 site. The B tetrahedron also shares two corners at the O7 site with

Mg1 octahedron and Si2 tetrahedron.

Summary

The atomic structures for the light elements standards phenakite, danburite,

spodumene, hambergite, lithiophilite, axinite and prismatine proposed by Dyar et al. (in

press) have been reported in this study. Cation substitutions and coordination for each

structure has also determined. SIMS, one of the major analytical tools, is dependant on

reference materials that are compositionally and structurally similar to the material in

question. This exemplifies the importance of the structural characterization of these

reference materials.

35 Referances

Burns P.C., Novák M. and Hawthorne F.C. (1995)

Fluorine-hydroxyl variation in hambergite: a crystal-structure study. Canadian

Mineralogist 33, 1205-1213.

Cameron M., Sueno S., Prewitt C.T. and Papike J.J. (1973)

High-temperature crystal chemistry of acmite, diopside, hedenbergite, jadeite, spodumene, and ureyite. American Mineralogist 58, 594-618.

Downs J.W. and Gibbs G.V. (1987)

An exploratory exanimation of the electron density and electrostatic potential of phenakite. American Mineralogist 72, 769-777.

Dyar M.D., Wiedenbeck M., Robertson D., Cross L.R., Delaney J.S., Ferguson K.,

Francis C.A., Grew E.S., Guidotti C.V., Hervig R.L., Hughes J.M., Husler J., Leeman

W., McGuire A.V., Rhede D., Rothe H., Paul R.L., Richards I. and Yates M. (in press)

Reference minerals for the microanalysis of light elements. Geostandards Newsletter:

The Journal of Geostandards and Geoanalysis 25.

Dyar M.D., Guidotti C.V., Grew E.S., Yates M., Delaney J.S., McGee J.J., McGuire

A.V., Paul R.L., Robertson, J.D., Cross L.R., Sisson V.M., Wiedenbeck M.W. and

Fowler G. (1998)

36 Interlaboratory comparison of tourmaline analyses: major elements including B, Li, and

Fe. Abstract to 17th International Mineralogical Association meeting, Toronto, paper

#494.

Frenz B.A. (1997)

SDP for Windows Reference Manual. B.A. Frenz & Associates, Inc. (College Station,

Texas) 201pp.

Grew E.S., Chernosky J.V., Werding G., Abraham K., Marquez N. and Hinthorne J.R.

(1990)

Chemistry of kornerupine and associated minerals, a wet chemical, ion microprobe, and

X-ray study emphasizing Li, Be, B and F contents. Journal of Petrology, 31, 1025-1070.

Klaska R. and Grew E.S. (1991)

The crystal structure of B-free kornerupine: Conditions favoring the incorporation of variable amounts of B through B ⇔ Si substitution in kornerupine. American

Mineralogist 76, 1824-1835.

Losey, A.B., Rakovan, J.F., Hughes, J.M., Francis, C.A. and Dyar, M.D. (submitted)

Structural variation in the phosphate olivine lithiophilite-triphylite series. Canadian

Mineralogist.

Phillips M.W., Gibbs G.V. and Ribbe P.H. (1974)

37 The crystal structure of danburite: a comparison with anorthite, albite, and reedmergnerite. American Mineralogist 59, 79-85.

Streltsov V.A., Belokoneva E.L., TsirelsonV.G. and Hansen N.K. (1993)

Multipole analysis of the electron density in triphylite, LiFePO4, using X-ray diffraction data. Acta Crystallographica B49, 147-153.

Swinnea J.S., Steinfink H., Rendon-DiazMiron L.E. and De La Vega S.E. (1981)

The crystal structure of a Mexican axinite. American Mineralogist 66, 428-431.

Table 2. Atomic positional parameters and isotropic B values for phenakite. Atom x y z B(Å) Be1 0.1941(1) 0.2099(1) 0.4150(2) 0.25(2) Be2 0.1939(1) 0.2116(1) 0.0838(2) 0.25(2) Si 0.19560(2) 0.21160(2) 0.74985(4) 0.228(5) O1 0.20982(6) 0.08842(6) 0.74971(9) 0.44(1) O2 0.33356(5) 0.33326(5) 0.7494(1) 0.40(1) O3 0.12243(6) 0.21013(6) 0.91532(8) 0.42(1) O4 0.12231(6) 0.20910(6) 0.58568(9) 0.42(1) Numbers in parentheses are the estimated standard deviations.

Table 3. Atomic positional parameters and isotropic B values for danburite. Atom x y z B(Å) Ca 0.38558(6) 0.25 0.07643(5) 0.690(7) B 0.2587(2) 0.4204(2) 0.4189(2) 0.51(3) Si 0.05332(5) -0.05577(6) 0.19245(5) 0.319(6) O1 0.1926(1) -0.0033(2) 0.0683(1) 0.71(2) O2 0.1263(1) -0.0422(2) 0.3651(1) 0.61(2) O3 0.3997(1) 0.0784(2) 0.3134(1) 0.59(2) O4 0.5136(2) 0.25 0.6639(2) 0.70(3) O5 0.1834(2) 0.25 0.4280(2) 0.70(3) Numbers in parentheses are the estimated standard deviations.

Table 4. Atomic positional parameters and isotropic B values for spodumene. Atom x y z B(Å) Li 0 0.2749(6) 0.25 1.36(8) Al 0 0.90671(8) 0.25 0.37(1) Si 0.29406(4) 0.09344(5) 0.25614(8) 0.441(7) O1 0.1098(1) 0.0822(1) 0.1410(2) 0.54(2) O2 0.3647(1) 0.2671(1) 0.3003(2) 0.76(2) O3 0.3566(1) 0.9868(2) 0.0585(2) 0.75(2) Numbers in parentheses are the estimated standard deviations.

Table 5. Atomic positional parameters and isotropic B values for hambergite. Atom x y z B(Å) Be1 0.0024(2) 0.1886(1) 0.2598(4) 0.69(2) Be2 0.2373(2) 0.0676(1) 0.2775(3) 0.69(2) B 0.1063(1) 0.1070(1) 0.7725(3) 0.65(2) O1 0.03753(9) 0.18770(6) 0.6192(2) 0.72(1) O2 0.10125(8) 0.10310(7) 0.0821(2) 0.70(1) O3 0.18674(8) 0.03450(7) 0.6172(2) 0.76(1) O4 0.33992(8) 0.17267(7) 0.2953(2) 0.87(1) H 0.818(2) 0.217(2) 0.067(5) 1.52(47)* Numbers in parentheses are the estimated standard deviations.

Table 6. Atomic positional parameters and isotropic B values for lithiophilite. Atom x y z B(Å) Li 0 0 0 1.59(8) Mn 0.28182(3) 0.25 0.97253(8) 0.558(5) P 0.09309(6) 0.25 0.4113(1) 0.550(9) O1 0.0968(2) 0.25 0.7343(4) 0.85(3) O2 0.4559(2) 0.25 0.2104(4) 0.86(3) O3 0.1624(1) 0.0487(2) 0.2787(2) 0.86(2) Numbers in parentheses are the estimated standard deviations.

Table 7. Atomic positional parameters and isotropic B values for axinite. Atom x y z B(Å) Si1 0.21152(8) 0.45040(6) 0.23491(6) 0.00782(12) Si2 0.21900(7) 0.27463(6) 0.52361(6) 0.00728(12) Si3 0.69909(8) 0.25585(6) 0.01124(6) 0.00828(12) Si4 0.64138(8) 0.01900(6) 0.23038(6) 0.00741(12) Fe 0.76837(4) 0.59095(4) 0.11238(4) 0.01151(12) Ca1 0.74630(6) 0.34813(4) 0.39531(4) 0.01119(10) Ca2 0.18284(6) 0.10059(4) 0.08391(4) 0.01197(10) Al1 0.05283(8) 0.80091(6) 0.25430(6) 0.00720(19) Al2 0.35212(8) 0.93605(6) 0.42121(6) 0.0065(2) B 0.4614(3) 0.6346(2) 0.2866(2) 0.0083(4) H 0.995(4) 0.961(3) 0.630(3) 0.018(7) O1 0.0549(2) 0.60349(15) 0.19029(15) 0.0103(3) O2 0.2321(2) 0.33866(16) 0.09639(16) 0.0129(3) O3 0.4196(2) 0.48744(15) 0.31272(16) 0.0104(3) O4 0.1361(2) 0.37286(17) 0.37058(16) 0.0136(3) O5 0.0215(2) 0.24255(15) 0.56399(15) 0.0096(3) O6 0.32649(19) 0.37969(15) 0.64528(15) 0.0098(3) O7 0.3806(2) 0.12756(15) 0.49582(15) 0.0089(3) O8 0.5363(2) 0.34386(16) 0.87716(15) 0.0105(3) O9 0.8765(2) 0.15474(15) 0.93334(15) 0.0094(3) O10 0.7692(2) 0.36620(16) 0.13899(16) 0.0127(3) O11 0.6039(2) 0.13435(16) 0.08690(16) 0.0126(3) O12 0.4363(2) 0.98135(15) 0.24411(15) 0.0094(3) O13 0.7206(2) 0.09991(16) 0.38455(15) 0.0094(3) O14 0.7942(2) 0.87411(16) 0.17805(15) 0.0102(3) O15 0.3250(2) 0.74668(15) 0.35443(15) 0.0084(3) O16 0.0969(2) 0.99543(15) 0.32273(15) 0.0090(3) Numbers in parentheses are the estimated standard deviations.

Table 8. Atomic positional parameters and isotropic B values for prismatine. Atom x y z B(Å) MgX 0 0 0 1.72(7) Mg1 0.12021(7) 0.14273(8) 0.25 0.73(2) Mg2 0.5 0.1470(1) 0.25 0.62(3) Al3 0.21551(6) 0 0 0.45(2) Al4 0.31249(6) 0.14227(7) 0.25 0.70(2) Al5 0.40915(6) 0 0 0.56(1) Si1 0.40138(5) 0.35293(6) 0.25 0.53(1) Si2 0.17443(6) 0.33465(6) 0.25 0.51(1) B3 0 0.3474(3) 0.25 0.99(6) O1 0.2241(1) 0.0455(2) 0.25 0.64(4) O2 0.4033(1) 0.0480(2) 0.25 0.64(4) O3 0.4008(1) 0.2354(2) 0.25 0.96(4) O4 0.1378(1) 0.0991(1) -0.0502(2) 0.87(3) O5 0.2289(1) 0.2371(2) 0.25 1.01(4) O6 0.31641(9) 0.0957(1) -0.0488(3) 0.76(3) O7 0.0775(1) 0.2878(2) 0.25 0.85(4) O8 0.5 0.0889(2) -0.0623(4) 0.69(4) O9 0 0.1135(3) 0.75 1.28(7) O10 0 0.0881(2) 0.25 0.98(6) Numbers in parentheses are the estimated standard deviations.