Aaron J. Lussier

Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: I. Crystal chemistry by SREF, EMPA, MAS NMR and Mössbauer spectroscopy

Abstract Tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, shows a variety of habits that resemble mushrooms, and it is commonly referred to as ‘mushroom tourmaline’. The structure of nine single crystals of elbaite, ranging in colour from pink to white to black and purple, extracted from two samples of mushroom tourmaline from Mogok, have been refined (SREF) to R indices of ~2.5% using graphite-monochromated Mo-Kα X-radiation. 11B and 27Al Magic Angle Spinning Nuclear Magnetic Resonance spectroscopy shows the presence of [4]B and the absence of [4]Al in samples with transition-metal content low enough to prevent paramagnetic quenching of the signal. Site populations were assigned from refined site-scattering values and unit formulae derived from electron-microprobe analyses of the crystals used for X-ray data collection. 57Fe Mössbauer spectroscopy shows that both Fe2+ and Fe3+ are present, and the site populations derived by structure refinement show that there is no Fe at the Z site; hence all Fe2+ and Fe3+ occurs at the Y site. The 57Fe Mössbauer spectra also show peaks due to intervalence charge-transfer involving Fe2+ and Fe3+ at adjacent Y sites. Calculation of the probability of the total amount of Fe occurring as Fe2+–Fe3+ pairs for a random short-range distribution is in close accord with the observed amount of Fe involved in Fe2+-Fe3+, indicating that there is no short-range order involving Fe2+ and Fe3+ in these tourmalines.

The occurrence of tetrahedrally coordinated Al and B in tourmaline: An 11B and 27Al MAS NMR study

Abstract Considerable uncertainty has surrounded the occurrence of tetrahedrally coordinated Al and B at the T site in tourmaline. Although previously detected in several tourmaline specimens, the frequency of these substitutions in nature, as well as the extent to which they occur in the tourmaline structure, is not known. Using 11B and 27Al MAS NMR spectroscopy, we have investigated the presence of B and Al at the T site in 50 inclusion-free tourmaline specimens of low transition-metal content and different species (elbaite, “fluor-elbaite” , liddicoatite, dravite, uvite, olenite, and magnesiofoitite) from different localities worldwide. Chemical shifts of [4]B and [3]B in 11B spectra, and [4]Al and [6]Al in 27Al spectra, are well resolved, allowing detection of even small amounts of T-site constituents. In the observed spectra, [4]B and [3]B peaks are located at 0 and 18-20 ppm, respectively, with the greatest intensity corresponding to [3]B (=3 apfu). In 27Al spectra, [4]Al and [6]Al bands are located at 68-72 and 0 ppm, respectively, with the greater intensity corresponding to [6]Al. However, inadequate separation of YAl and ZAl precludes resolution of these two bands. Simulation of 11B MAS NMR spectra shows that tetrahedrally and trigonally coordinated B can be readily distinguished at 14.1 T and that a [4]B content of 0.0-0.5 apfu is common in tourmaline containing low amounts of paramagnetic species. 27Al MAS NMR spectra show that Al is also a common constituent of the T site in tourmaline. Determination of [4]Al content by peak-area integration commonly shows values of 0.0-0.5 apfu. Furthermore, the chemical shift of the 27Al tetrahedral peak is sensitive to local order at the adjacent Y and Z octahedra, where [4]Al-YMg3 and [4]Al-Y(Al,Li)3 arrangements result in peaks located at ~65 and ~75 ppm, respectively. Both 11B MAS NMR and 27Al MAS NMR spectra show peak broadening as a function of transition-metal content (i.e., Mn2+ + Fe2+ = 0.01-0.30 apfu) in the host tourmaline. In 11B spectra, broadening and loss of intensity of the [3]B signal ultimately obscures the signal corresponding to [4]B, increasing the limit of detection of [4]B in tourmaline. Our results clearly show that all combinations of Si, Al, and B: T = (Al, Si)6, T = (B, Si)6, T = (Al, B, Si)6, and T = Si6 apfu, are common in natural tourmalines.

Elbaite-liddicoatite from Black Rapids glacier, Alaska

Periodico di Mineralogia (2011), 80, 1 (Special Issue), 57-73 - DOI: 10.2451/2011PM0005 Special Issue in memory of Sergio Lucchesi Elbaite-liddicoatite from Black Rapids glacier, Alaska Aaron J. Lussier 1 , Frank C. Hawthorne 1,* , Vladimir K. Michaelis 2 , Pedro M. Aguiar 2 and Scott Kroeker 2 1 Department of Geological Sciences, University of Manitoba, Winnipeg, Canada 2 Department of Chemistry, University of Manitoba, Winnipeg, Canada *Corresponding author: frank_hawthorne@umanitoba.ca Abstract Liddicoatite, ideally Ca(AlLi 2 )Al 6 (SiO 6 )(BO 3 ) 3 (OH) 3 F, is an extremely rare species of tourmaline, found in very few localities worldwide. A large (~ 2 cm in cross section), euhedral sample of tourmaline retrieved from atop the Black Rapids glacier, Alaska, is shown to vary from a light pink elbaite in the core region, average composition (Na 0.4 Ca 0.3□0.3 )(Al 1.75 Li 1.25 ) Al 6 (BO 3 ) 3 (Si 6 O 18 )F 0.4 (OH) 3.6 , to a pale green liddicoatite at the edge of the crystal, (Na 0.3 Ca 0.6 □ 0.1 )(Al 1.0 Li 1.6 Fe 0.2 Mn 0.2 )Al 6 (BO 3 ) 3 (Si 6 O 18 )F 1.0 (OH) 3.0 . Detailed electron-microprobe analysis and 11 B and 27 Al Magic-Angle-Spinning Nuclear Magnetic Resonance spectroscopy show that several substitutions were active during growth, with X □ + Y Al → X Ca + Y Li (liddicoatite-rossmanite solid-solution) and 2 Y Al + X □ → 2 Y M* + X Ca accounting for most of the compositional variation. Throughout the tourmaline, there are instances of reversals in the trends of all major constituents, although few compositional gaps are observed. Most notably, a sharp decline in Ca content from ~ 0.35 to ~ 0.05 apfu (atoms per formula unit) with increasing distance from the core at ~ 2 mm from the crystal edge is followed by a sharp rise in Ca content (to 0.55 apfu), along with (Fe + Mn) content (from 0.01 to 0.35 apfu). In the core region, the origin of the Ca in the tourmaline is not clear; the correlation of Ca and F is consistent with both (1) a melt in which Ca was held as complexes with F, or (2) earlier contamination of the melt by a (Ca, F)-rich fluid. Close to the rim, a dramatic increase in Ca, F, Mn and Fe is probably due to late-stage contamination by fluids that have removed these components from adjacent wallrocks. Key words: liddicoatite; elbaite; tourmaline; late-stage Ca enrichment; pegmatite; zoning; electron-microprobe analysis; Black Rapids glacier, Alaska; 11 B MAS NMR; 27 Al MAS NMR.

Fluor-elbaite, Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3F, a new mineral species of the tourmaline supergroup

Abstract Fluor-elbaite, Na(Li1.5Al1.5)Al6(Si6O18)(BO3)3(OH)3F, is a new mineral of the tourmaline supergroup. It is found in miarolitic cavities in association with quartz, pink muscovite, lepidolite, spodumene, spessartine, and pink beryl in the Cruzeiro and Urubu mines (Minas Gerais, Brazil), and apparently formed from late-stage hydrothermal solutions related to the granitic pegmatite. Crystals are bluegreen with a vitreous luster, sub-conchoidal fracture and white streak. Fluor-elbaite has a Mohs hardness of approximately 7.5, and has a calculated density of about 3.1 g/cm3. In plane-polarized light, fluor-elbaite is pleochroic (O = green/bluish green, E = pale green), uniaxial negative. Fluor-elbaite is rhombohedral, space group R3̄m, a = 15.8933(2), c = 7.1222(1) Å, V = 1558.02(4) Å3, Z = 3 (for the Cruzeiro material). The strongest eight X-ray-diffraction lines in the powder pattern [d in Å(I)(hkl)] are: 2.568(100)(051), 2.939(92)(122), 3.447(67)(012), 3.974(58)(220), 2.031(57)(152), 4.200(49)(211), 1.444(32)(642), and 1.650(31)(063). Analysis by a combination of electron microprobe, secondary ion mass spectrometry, and Mössbauer spectroscopy gives SiO2 = 37.48, Al2O3 = 37.81, FeO = 3.39, MnO = 2.09, ZnO = 0.27, CaO = 0.34, Na2O = 2.51, K2O = 0.06, F = 1.49, B2O3 = 10.83, Li2O = 1.58, H2O = 3.03, sum 100.25 wt%. The unit formula is: X(Na0.78□0.15Ca0.06K0.01)Y(Al1.15Li1.02Fe2+ 0.46Mn2+ 0.28Zn0.03) ZAl6 T(Si6.02O18)B(BO3)3V(OH)3W(F0.76OH0.24). The crystal structure of fluor-elbaite was refined to statistical indices R1 for all reflections less then 2% using MoKα X-ray intensity data. Fluor-elbaite shows relations with elbaite and tsilaisite through the substitutions WF ↔ WOH and Y(Al + Li) + WF ↔ 2YMn2+ + WOH, respectively.

Mushroom elbaite from the Kat Chay mine, Momeik, near Mogok, Myanmar: II. Zoning and crystal growth

Abstract A variety of mushroom tourmaline from the Kat Chay mine, Momeik, near Mogok, Shan state, Myanmar, consists of a black-to-grey single-crystal core from which a single prismatic crystal reaches to the edge of the mushroom, forming a slight protuberance. The rest of the mushroom (~50% by volume) consists of extremely acicular sub-parallel crystals that diverge toward the edge of the mushroom. The acicular crystals are dominantly colourless to white, with a continuous black zone (2 mm across) near the edge, and pale pink outside the black zone. The composition varies from ~Na0.75Ca0.05(Li0.80Al0.70Fe1.10Mn0.30Ti0.10) Al6Si6(BO3)3O18(OH)3(OH,F) at the base of the mushroom to ~Na0.60Ca0.06(Li1.00Al1.98Fe0.02)Al6(Si5.35 B0.65)(BO3)3O18(OH)3(OH,F) close to the edge at the top of the mushroom. The principal substitutions are: (1) YLi + YAl → YFe* + YFe* and (2) TB + YAl → Si + YFe*, but there are five other minor substitutions that are also operative. There are six significant compositional discontinuities at textural boundaries in the mushroom, suggesting that the changes in habit are driven in part by changes in external variables such as T and P, plus possible involvement of new fluid phases.

Maruyamaite, K(MgAl2)(Al5Mg)Si6O18(BO3)3(OH)3O, a potassium-dominant tourmaline from the ultrahigh-pressure Kokchetav massif, northern Kazakhstan: Description and crystal structure

Abstract Maruyamaite, ideally K(MgAl2)(Al5Mg)Si6O18(BO3)3(OH)3O, was recently approved as the first K-dominant mineral-species of the tourmaline supergroup. It occurs in ultrahigh-pressure quartzofeldspathic gneisses of the Kumdy-Kol area of the Kokchetav Massif, northern Kazakhstan. Maruyamaite contains inclusions of microdiamonds, and probably crystallized near the peak pressure conditions of UHP metamorphism in the stability field of diamond. Crystals occur as anhedral to euhedral grains up to 2 mm across, embedded in a matrix of anhedral quartz and K-feldspar. Maruyamaite is pale brown to brown with a white to very pale-brown streak and has a vitreous luster. It is brittle and has a Mohs hardness of ∼7; it is non-fluorescent, has no observable cleavage or parting, and has a calculated density of 3.081 g/cm3. In plane-polarized transmitted light, it is pleochroic, O = darkish brown, E = pale brown. Maruyamaite is uniaxial negative, ω = 1.634, ε = 1.652, both ±0.002. It is rhombohedral, space group R3m, a = 15.955(1), c = 7.227(1) Å, V = 1593(3) Å3, Z = 3. The strongest 10 X-ray dif- fraction lines in the powder pattern are [d in Å(I)(hkl)]: 2.581(100)(051), 2.974(85)(1̄32), 3.995 (69)(2̄40), 4.237(59)(2̄31), 2.046(54)(1̄62), 3.498(42)(012), 1.923(36)(3̄72), 6.415(23)(1̄11), 1.595(22)(5̄.10.0), 5.002(21)(021), and 4.610(20)(030). The crystal structure of maruyamaite was refined to an R1 index of 1.58% using 1149 unique reflections measured with MoKα X-radiation. Analysis by a combination of electron microprobe and crystal-structure refinement gave SiO2 36.37, Al2O3 31.50, TiO2 1.09, Cr2O3 0.04, Fe2O3 0.33, FeO 4.01, MgO 9.00, CaO 1.47, Na2O 0.60, K2O 2.54, F 0.30, B2O3(calc) 10.58, H2O(calc) 2.96, sum 100.67 wt%. The formula unit, calculated on the basis of 31 anions pfu with B = 3, OH = 3.24 apfu (derived from the crystal structure) and the site populations assigned to reflect the mean interatomic distances, is (K0.53Na0.19Ca0.26□0.02)ΣX=1.00(Mg1.19Fe0.552+Fe0.053+

The crystal chemistry of ‘wheatsheaf’ tourmaline from Mogok, Myanmar

{\rm{Fe}}_{0.55}^{2 + }{\rm{Fe}}_{0.05}^{3 + }

Triclinic titanite from the Heftetjern granitic pegmatite, Tørdal, southern Norway

Ti0.14Al1.07)□Y=3.00(Al5.00Mg1.00)(Si5.97Al0.03O18)(BO3)3(OH)3(O0.602−

Short-range constraints on chemical and structural variations in bavenite

{\rm{O}}_{0.60}^{2 - }

Oscillatory zoned liddicoatite from Anjanabonoina, central Madagascar. I. Crystal chemistry and structure by SREF and 11B and 27Al MAS NMR spectroscopy

F0.16OH0.24). Maruyamaite, ideally K(MgAl2) (Al5Mg)(BO3)3(Si6O18)(OH)3O, is related to oxy-dravite: ideally Na(MgAl2)(Al5Mg)(BO3)3(Si6O18)(OH)3O, by the substitution XK → XNa.