Yassir A. Abdu

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.

Mineralogy and Weathering of Smelter-Derived Spherical Particles in Soils: Implications for the Mobility of Ni and Cu in the Surficial Environment

Spherical particles have been sampled from soils and silica-rich rock coatings close to major smelter centers at Coppercliff, Coniston, and Falconbridge in the Sudbury area, Canada. Detailed analyses employing optical microscopy, scanning electron microscopy, transmission electron microscopy, micro-Raman spectroscopy, and Mössbauer spectroscopy have been conducted to elucidate their nature, origin and potential alteration. The spherical particles are on the nano- to millimeter-size range and are composed principally of magnetite, hematite, Fe-silicates (olivine, pyroxenes), heazlewoodite, bornite, pyrrhotite, spinels (including trevorite and cuprospinel), delafossite, and cuprite or tenorite. The spinels present have variable Cu and Ni contents, whereas delafossite and cuprite are Ni free. Texturally, the spherical particles are composed of a Fe-oxide–Fe-silicate matrix with sulfide inclusions. The matrix displays growth features of a Fe-rich phase that commonly form during rapid cooling and transformation processes within smelter and converter facilities. Examination of weathered spherical particles indicates that some sulfide inclusions have dissolved prior to the alteration of the Fe-silicates and oxides and that the weathering of Fe-silicates occurs simultaneously with the transformation of magnetite into hematite. A higher proportion of Cu vs. Ni in the clay and organic fraction noted in the Sudbury soils is explained by (1) the formation of stronger adsorption complexes between Cu and the corresponding surface species and (2) the preferential release of Cu vs. Ni by smelter-derived particles. The latter mechanism is based on the observations that (a) cuprospinels have higher dissolution rates than Ni spinels, (b) a larger proportion of Cu occurs in the nanometer-size (and thus more soluble) fraction of the emitted particles, and (c) Ni spinels of relatively low solubility form in the alteration zone of heazlewoodite inclusions.

Hydrous silica coatings: occurrence, speciation of metals, and environmental significance.

Si-enriched coatings form on the surface of silicate minerals under acidic conditions. Although they are often only a few nanometers thick, their large specific surface area may control the interaction between silicate minerals in acidic soils, aquifers, and mine tailings. Micrometer thick, hydrous-silica coatings occur on the surface of a granite outcrop in contact with acidic pond water at the Coppercliff mine-tailings area in the Greater City of Sudbury, Ontario, and are ideal to study the concentration and speciation of metals and metalloids inside Si-enriched coatings. These coatings have higher average concentrations of Cr, Mn, Co, Ni, Cu, Zn, and Pb than coatings composed of schwertmannite, Fe(8)O(8)(OH)(4.4)(SO(4))(1.8) (H(2)O)(8.4). Microscopic and spectroscopic examination of the hydrous-silica coating indicates the occurrence of Fe- and Cu-Zn-oxy-hydroxide particles, tetrahedrally coordinated Fe(3+) and a high proportion of M-O-Si bonds (M = metal). These observations suggest that metals occur either finely distributed in the hydrous-silica matrix or in oxy-hydroxide particles. The latter particles are products of the diffusion of metals into the hydrous silica and the subsequent nucleation of oxy-hydroxide phases.

From structure topology to chemical composition. VII. Titanium silicates: the crystal structure and crystal chemistry of jinshajiangite

The crystal structure of jinshajiangite, ideally BaNaTi 2 Fe 4 2+ (Si 2 O 7 ) 2 O 2 (OH) 2 F, a 10.6785(8), b 13.786(1), c 20.700(2) A, β 94.937(1)°, V 3035.93(6) A 3 , sp. gr. C 2/ m , Z = 8, D calc. 3.767 g/cm 3 , from Norra Karr, Tonkoping province, Sweden, has been refined to R 1 5.69 % on the basis of 3193 unique reflections (F O > 4σF). Electron microprobe analysis gave (wt%): SiO 2 27.56, Nb 2 O 5 0.12, TiO 2 18.36, ZrO 2 0.51, FeO 23.42, Fe 2 O 3 2.89 [the Fe 3+ /Fe tot ratio of 0.10(9) was determined by Mossbauer spectroscopy], MnO 5.13, MgO 0.44, CaO 2.52, BaO 10.24, K 2 O 1.95, Na 2 O 2.27, F 2.33, H 2 O 2.00 (calc. from structure refinement: OH + F = 3 apfu ), O = F − 0.98, total 98.76. The empirical formula is (Ba 0.58 K 0.36 ) ∑0.94 (Na 0.57 Ca 0.39 ) ∑0.96 (Fe 2.84 2+ Mn 0.63 Fe 0.32 3+ Mg 0.10 Zr 0.04 Na 0.07 ) ∑4.00 (Ti 2.00 Nb 0.01 ) ∑2.01 (Si 2 O 7 ) 2 O 2.12 (OH) 1.93 F 1.07 , calculated on the basis of 4 Si apfu . The crystal structure of jinshajiangite can be described as a combination of a TS block and an I block. The TS (titanium silicate) block consists of HOH sheets (H-heteropolyhedral, O-octahedral), and is a component of 27 Ti-disilicate minerals. In the O sheet, there are five [6]-coordinated M O sites occupied mainly by Fe 2+ and Mn 2+ , with minor Fe 3+ , Mg, Zr and Na with O –O> = 2.175 A. Five M O sites give ideally Fe 2+ 4 pfu . In the H sheet, there are three [6]-coordinated M H sites occupied solely by Ti (Ti = 2 apfu ), with H –O>. = 1.953 A, and four [4]-coordinated Si sites occupied solely by Si, with . = 1.619 A. The M H octahedra and (Si 2 O 7 ) groups constitute the H sheet. Linkage of H and O sheets via common vertices of M H octahedra and (Si 2 O 7 ) groups with M O (1–5) octahedra results in a TS block. The topology of the TS block is as in Group II of the Ti disilicates (Ti = 2 apfu ). There are six interstitial sites, three [9–10]-coordinated Ba-dominant A P sites with P –O> = 2.98 A and three [10]-coordinated Na-dominant B P sites with P –O> = 2.600 A. The total content of three A P sites sums to ~1 apfu = Ba 0.58 K 0.36 or ideally 1 Ba pfu . The total content of the three B P sites is Na 0.57 Ca 0.39 or ideally 1 Na pfu . Along c , the TS blocks link via common vertices of M H octahedra (as in astrophyllite-group minerals) and A P and B P sites which constitute the I block. Jinshajiangite is an Fe 2+ analogue of perraultite, ideally BaNaTi 2 Mn 4 2+ (Si 2 O 7 ) 2 O 2 (OH) 2 F, and its crystal structure is topologically identical to that of perraultite.

From structure topology to chemical composition. IX. Titanium silicates : revision of the crystal chemistry of lomonosovite and murmanite, Group-IV minerals

Abstract The crystal structures of lomonosovite, ideally Na10Ti4(Si2O7)2(PO4)2 O4, a = 5.4170(7) Å, b = 7.1190(9) Å, c = 14.487(2) Å, α = 99.957(3)º, β = 96.711(3)º, γ = 90.360(3)º, V = 546.28(4) Å3, Dcalc. = 3.175 g cm-3, and murmanite, ideally Na4Ti4(Si2O7)2O4(H2O)4, a = 5.3875(6) Å, b = 7.0579(7) Å, c = 12.176(1) Å, α = 93.511(2)º, β = 107.943(4)º, γ = 90.093(2)º, V = 439.55(2) Å3, Dcalc. = 2.956 g.cm-3, from the Lovozero alkaline massif, Kola Peninsula, Russia, have been refined in the space group P1̅ (Z = 1) to R values of 2.64 and 4.47%, respectively, using 4572 and 2222 observed |Fo ≥ 4σF| reflections collected with a single-crystal Bruker AXS SMART APEX diffractometer with a CCD detector and Mo-Kα radiation. Electron microprobe analysis gave empirical formulae for lomonosovite (Na9.50Mn0.16Ca0.11)∑9.77(Ti2.834+Nb0.51Mn0.272+Zr0.11Mg0.11Fe0.102+Fe0.063+Ta0.01)∑4.00(Si2.02O7)2 (P0.98O4)2(O3.50F0.50)∑4, Z = 1, calculated on the basis of 26(O+F) a.p.f.u., and murmanite (Na3.32Mn0.15Ca0.21K0.05)∑3.73(Ti3.084+Nb0.51Mn0.182+Fe0.153+Mg0.07Zr0.01)∑4.00(Si1.98O7)2(O3.76F0.24)∑4 (H2O)4, Z = 1, calculated onthe basis of 22(O+F) a.p.f.u., with H2O determined from structure refinement and Fe3+/(Fe2++Fe3+) ratios obtained by Mössbauer spectroscopy. The crystal structures of lomonosovite and murmanite are a combination of a titanium silicate (TS) block and an intermediate (I) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral), and is characterized by a planar cell based on translation vectors, t1 and t2, with t1 ~5.5 and t2 ~7 Å and t1 ^ t2 close to 90º. The TS block exhibits linkage and stereochemistry typical for Group IV (Ti = 4 a.p.f.u.) of the Ti disilicate minerals: two H sheets connect to the O sheet such that two (Si2O7) groups link to Ti polyhedra of the O sheet adjacent along t1. In murmanite and lomonosovite, the invariant part of the TS block is of composition Na4Ti4(Si2O7)2O4. There is no evidence of vacancydominant cation sites or (OH) groups in the O sheet of lomonosovite or murmanite. In lomonosovite, the I block is a framework of Na polyhedra and P tetrahedra which gives 2[Na3 (PO)4] p.f.u. In murmanite, there are four (H2O) groups in the intermediate space between TS blocks. In lomonosovite, TS and I blocks alternate along c. In murmanite, TS blocks are connected via hydrogen bonding. The H atoms were located and details of the hydrogen bonding are discussed.

Cámaraite, Ba3NaTi4(Fe2+,Mn)8(Si2O7)4O4(OH,F)7. I. A new Ti-silicate mineral from the Verkhnee Espe Deposit, Akjailyautas Mountains, Kazakhstan

Abstract Cámaraite, ideally Ba3NaTi4(Fe2+,Mn)8(Si2O7)4O4(OH,F)7, is a new mineral from the Verkhnee Espe deposit, Akjailyautas Mountains, Kazakhstan. It occurs as intergrowths with bafertisite and jinshajiangite in separate platy crystals up to 8 mm × 15 mm × 2 mm in size, or as star-shaped aggregates of crystals with different orientations. Individual crystals are orange-red to brownish-red, and are platy on {001}. Cámaraite is translucent and has a pale-yellow streak, a vitreous lustre, and does not fluoresce under cathode or ultraviolet light. Cleavage is {001} perfect, no parting was observed, and Mohs hardness is <5; the mineral is brittle. The calculated density is 4.018 g cm−3. In transmitted light, cámaraite is strongly pleochroic, X = light brown, Y = reddish-brown, Z = yellow-brown, with Z < X < Y. Cámaraite is biaxial +ve and 2Vmeas. = 93(1)°. All refractive indices are greater than 1.80. Cámaraite is triclinic, space group C 1̅, a = 10.678(4) Å, b = 13.744(8) Å, c = 21.40(2) Å, α = 99.28(8)°, β = 92.38(5)°, γ = 90.00(6)°, V = 3096(3) Å3, Z = 4, a:b:c = 0.7761:1:1.5565. The seven strongest lines in the X-ray powder-diffraction pattern are as follows: [d (Å), (I), (hkl)]: 2.63, (100), (401); 2.79, (90), (2̅4̅3, 2̅41, 22̅6, 225); 1.721, (70), (2̅4̅11, 2̅49, 08̅2); 3.39, (50), (22̅4, 223); 3.18, (50), (2̅2̅5, 2̅24); 2.101, (50), (4̅4̅2, 4̅40); 1.578, (50), (6̅4̅1, 6̅4̅2, 64̅1, 6̅40). Chemical analysis by electron microprobe gave: Nb2O5 1.57, SiO2 25.25, TiO2 15.69, ZrO2 0.33, Al2O3 0.13, Fe2O3 2.77, FeO 16.54, MnO 9.46, ZnO 0.12, MgO 0.21, CaO 0.56, BaO 21.11, Na2O 1.41, K2O 0.84, H2O 1.84, F 3.11, less O≡F 1.31, total 99.63 wt.%, where the valence state of Fe was determined by Mössbauer spectroscopy [Fe3+/(Fe2+ + Fe3+) = 0.13(8)] and the H2O content was derived by crystal-structure determination. The resulting empirical formula on the basis of 39 anions is (Ba2.61K0.34)Σ2.95(Na0.86Ca0.14)Σ1(Ti3.72Nb0.22Al0.05)Σ3.99(Fe2+4.36Fe3+0.66Mn2.53Mg0.10Zr0.05Zn0.03Ca0.05)Σ7.78Si7.97O35.89H3.88F3.11. Cámaraite is a Group-II TS-block mineral in the structure hierarchy of Sokolova (2006). The mineral is named cámaraite after Fernando Cámara (born 1967) of Melilla, Spain, in recognition of his contribution to the fields of mineralogy and crystallography. The new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, International Mineralogical Association (IMA 2009-11).

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.

Sveinbergeite, Ca(Fe2+6 Fe3+)Ti2(Si4O12)2O2(OH)5(H2O)4, a newastrophyllite-group mineral from the Larvik Plutonic Complex, Oslo Region, Norway: description and crystal structure

Abstract Sveinbergeite, Ca(Fe62+Fe3+)Ti2(Si4O12)2O2(OH)5(H2O)4, is a new astrophyllite-group mineral discovered in a syenite pegmatite at Buer on the Vesterøya peninsula, Sandefjord, Oslo Region, Norway. The mineral occurs in pegmatite cavities as 0.01-0.05 mm thick lamellar (0.2-0.5 × 5-10 mm) crystals forming rosette-like divergent groups and spherical aggregates, which are covered by brown coatings of iron (and possibly manganese) oxides, associated with magnesiokatophorite, aegirine, microcline, albite, calcite, fluorapatite, molybdenite, galena and a hochelagaite-like mineral. Crystals of sveinbergeite are deep green with a pale green streak and a vitreous and pearly lustre. Sveinbergeite has perfect cleavage on {001} and a Mohs hardness of 3. Its calculated density is 3.152 g/cm3. It is biaxial positive with α 1.745(2), β 1.746(2), γ 1.753(2), 2V(meas.) = 20(3)º. The mineral is pleochroic according to the scheme Z > X ~ Y : Z is deep green, X and Y are brownish green. Orientation is as follows: X ⊥ (001), Y ^ b = 12º, Z = a, elongation positive. Sveinbergeite is triclinic, space group P1̄, a = 5.329(4), b = 11.803(8), c = 11.822(8) Å; α = 101.140(8)º, β = 98.224(8)º, γ = 102.442(8)º; V = 699.0(8) Å3; Z = 1. The nine strongest lines in the X-ray powder diffraction pattern [d in Å (I)(hkl)] are: 11.395(100)(001,010), 2.880(38)(004), 2.640(31)(2̄10,1̄41), 1.643(24)(07̄1,07̄2), 2.492(20)(21̄1), 1.616(15)(070), 1.573(14)(3̄2̄2), 2.270(13)(1̄3̄4) and 2.757(12)(1̄40,1̄32). Chemical analysis by electron microprobe gave Nb2O5 0.55, TiO2 10.76, ZrO2 0.48, SiO2 34.41, Al2O3 0.34, Fe2O3 5.57, FeO 29.39, MnO 1.27, CaO 3.87, MgO 0.52, K2O 0.49, Na2O 0.27, F 0.24, H2O 8.05, O=F -0.10, sum 96.11 wt.%, the amount of H2O was determined from structure refinement, and the valence state of Fe was calculated from structure refinement in accord with Mössbauer spectroscopy. The empirical formula, calculated on the basis of eight (Si + Al) p.f.u., is (Ca0.95Na0.12K0.14)∑1.21(Fe5.652+Fe0.933+Mn0.25Mg0.18)∑7.01(Ti1.86Nb0.06Zr0.05Fe0.033+)∑2(Si7.91Al0.09)∑8O34.61H12.34F0.17, Z = 1. The infrared spectrum of the mineral contains the following absorption frequencies: 3588, ~3398 (broad), ~3204 (broad), 1628, 1069, 1009, 942, 702, 655 and 560 cm-1. The crystal structure of the mineral was solved by direct methods and refined to an R1 index of 21.81%. The main structural unit in the sveinbergeite structure is an HOH layer which is topologically identical to that in the astrophyllite structure. Sveinbergeite differs from all other minerals of the astrophyllite group in the composition and topology of the interstitial A and B sites and linkage of adjacent HOH layers. The mineral is named in honour of Svein Arne Berge (b. 1949), a noted Norwegian amateur mineralogist and collector who was the first to observe and record this mineral from its type locality as a potential new species.

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.

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

Abstract Tourmalines of unusual (mushroom) habit are common in granitic pegmatites of Momeik, northeast of Mogok, Myanmar. Here, we examine a sample of elbaite of significantly different habit, consisting of a series of diverging crystals, resembling a sheaf of wheat and ranging in colour from light purplish-red at the base to dark purplish-red at the tip with a thin green cap at the termination. The crystal structures of eight crystals are refined to R1-indices of ~2.5% using graphite-monochromated Mo-Kα X-radiation; the same crystals were analysed by electron microprobe. 11B and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra were collected on four regions of the wheatsheaf crystal, and show ~0.3 a.p.f.u. [4]B and <0.1 a.p.f.u. [4]Al in the structure. 57Fe Mössbauer spectroscopy was done on the dark green rim at the termination of the crystal, showing all Fe in this region (~0.6 a.p.f.u.) to be Fe2+. Detailed electron-microprobe traverses show that the principal compositional variation involves the substitutions [4]B + YAl → Si + YFe*, where transition metals are present, and [4]B2 + YAl → Si2 + YLi, where transition metals are not present, although several other minor substitutions also affect crystal composition. Successive microscopic bifurcation of crystallites causes divergence of growth directions along the c axis, imparting the overall ‘wheatsheaf’ shape to the crystal aggregate. We suggest that such bifurcation is common in pegmatitic elbaite crystals, resulting in their common divergent habit.