Tashelgite, CaMgFe2 + Al9O16(OH), a new mineral species from calc-skarnoid in Gorny Shoria

A new mineral species has been discovered at the calc-skarnoid occurrence near the mouth of the Tashelga River, Kuznetsky Alatau, Gorny Shoria, Russia, and named after the locality of its discovery. Associated minerals are calcite, hibonite, grossular, vesuvianite, hercynite, magnetite, corundum, perovskite, scapolite, diopside, and apatite. The new mineral occurs as prismatic or finely fibrous crystals up to 1.5–2.0 mm in length, their parallel intergrowths, and felty aggregates as large as 10 mm across. Tashelgite is bluish green, translucent to transparent, with vitreous luster; D _calc = 3.67 g/cm³. The IR spectrum does not contain bands of OH groups. Tashelgite is biaxial (−), with α = 1.736(2), β = 1.746(2), γ = 1.750(2); 2V _meas = −20(2)°. Dispersion is strong, r < ν. Pleochroism is distinct: X (blue-green) > Y (yellowish green) > Z (almost colorless). Chemical composition (electron microprobe, average of five-point analyses, Fe₂O₃ is estimated from the ratio of intensities I(Fe_Kb5 )/I(Fe_Kb1 )I(Fe_{K\beta _5 } )/I(Fe_{K\beta _1 } ) in the X-ray spectrum, H₂O was determined as a weight loss on heating in vacuum up to 1000°C), wt %: 7.98 CaO, 6.75 MgO, 0.45 MnO, 11.32 FeO, 1.40 Fe₂O₃, 70.70 Al₂O₃, 1.8(2) H₂O, 100.40 in total. The empirical formula calculated on the basis of 17 oxygen atoms is H_1.27Ca_0.90Mg_1.06Mn_0.04 Fe_1.00²⁺Fe_0.11³⁺Al_8.80O_17.00. The idealized formula is CaMgFe²⁺Al₉O₁₆(OH). According to single-crystal X-ray structural data, tashelgite is monoclinic, pseudoorthorhombic, space group Pc; unit cell parameters are: a = 5.6973(1), b = 17.1823(4), c = 23.5718(5)?; β = 90.046(3)°; V = 2307.5(1)?³, Z = 8. The crystal structure of tashelgite is unique and characterized by ordering of all cations; Al occupies sites with octahedral and tetrahedral coordination. The cation ordering has also been confirmed by IR spectroscopy. The strongest lines of the X-ray powder diffraction pattern (d, ?]-I[hkl] are: 11.79–48 [002], 2.845–43 [061], 2.616–100 [108], 2.584–81 [146], 2.437–44 [163], 2.406–61 [057], 2.202–72 [244]. The type specimen of tashlegite has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia.     

Dualite, Na30(Ca,Na,Ce,Sr)12(Na,Mn,Fe,Ti)6Zr3Ti3MnSi51O144(OH,H2O,Cl)9, a new zircono-titanosilicate with a modular eudialyte-like structure from the Lovozero alkaline Pluton, Kola Peninsula, Russia

Dualite has been found at Mount Alluaiv, the Lovozero Pluton, the Kola Peninsula in peralkaline pegmatoid as sporadic, irregularly shaped grains up to 0.3–0.5 mm across. K-Na feldspar, nepheline, sodalite, cancrinite, aegirine, alkaline amphibole, eudialyte, lovozerite, lomonosovite, vuonnemite, lamprophyllite, sphalerite, and villiaumite are associated minerals. Dualite is yellow, transparent or translucent, with conchoidal fracture. The new mineral is brittle, with vitreous luster and white streaks. The Mohs hardness is 5. The measured density is 2.84(3) g/cm₃ (volumetric method); the calculated density is 2.814 g/cm₃. Dualite dissolves and gelates in acid at room temperature. It is nonfluorescent. The new mineral is optically uniaxial and positive; ω = 1.610(1), ɛ = 1.613(1). Dualite is trigonal, space group R3m. The unit cell dimensions are a = 14.153(9), c = 60.72(5) ?, V = 10533(22) ?, Z = 3. The strongest reflections in the X-ray powder pattern [d, ? (I,%)(hkl)] are as follows: 7.11(40)(110), 4.31(50)(0.2.10), 2.964(100)(1.3.10), 2.839(90)(048), 2.159(60)(2.4.10, 0.4.20), 1.770(60)(2.4.22, 4.0.28, 440), 1362(50)(5.5.12, 3.0.42). The chemical composition (electron microprobe, H₂O calculated from X-ray diffraction data) is as follows, wt %: 17.74 Na₂O, 0.08 K₂O, 8.03 CaO, 1.37 SrO, 0.29 BaO, 2.58 MnO, 1.04 FeO, 0.79 La₂O₃, 1.84 C₂O₃, 0.88 Nd₂O₃, 0.20 Al₂O₃, 51.26 SiO₂, 4.40 TiO₂, 5.39 ZrO₂, 1.94 Nb₂O₅, 0.58 Cl, 1.39 H₂O,-O = 0.13 Cl₂; they total is 99.67. The empirical formula calculated on the basis of 106 cations as determined by crystal structure is (Na_29.79Ba_0.1K_0.10)_Σ30(Ca_8.55Na_1.39REE_1.27Sr_0.79)_Σ12 · (Na_3.01Mn_1.35Fe_0.87²⁺Ti_0.77)_Σ6(Zr_2.61Nb_0.39)_Σ3 (Ti_2.52Nb_0.48)_Σ3(Mn_0.82Si_0.18)_Σ1(Si_50.77Al_0.23)_Σ51 O₁₄₄[(OH)_6.54(H₂O)_1.34·Cl_0.98]_Σ8.86). The simplified formula is Na₃₀(Ca,Na,Ce,Sr)₁₂(Na,Mn,Fe,Ti)₆Zr₃Ti₃ MnSi₅₁O₁₄₄ (OH,H₂O,Cl)₉). The name dualite is derived from Latin dualis (dual) alluding to the dual taxonomic membership of this mineral, which is at the same time zirconosilicate and titanosilicate. The crystal structure is characterized by two module types (alluivite-like and eudialyte-like) alternating along a threefold axis with a doubled c period relative to eudialyte and close chemical affinity to rastsvetaevite (Khomyakov et al., 2006a) and labyrynthite (Khomyakov et al., 2006b). According to the authors’ crystal chemical taxonomy of the eudialyte group, the new mineral belongs to one of three subgroups characterized by a 24-layered structural framework. Dualite is a mineral formed during the final stages of peralkaline pegmatite formation. The type material of dualite is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? A.P. Khomyakov, G.N. Nechelyustov, R.K. Rastsvetaeva, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, Pt CXXXVI, No. 4, pp. 68–73. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, July 8, 2005.     

Phosphoinnelite, Ba4Na3Ti3Si4O14(PO4,SO4)2(O,F)3, a new mineral species from peralkaline pegmatite of the Kovdor pluton, Kola Peninsula

Phosphoinnelite, an analogue of innelite with P > S, has been found in a peralkaline pegmatite vein crosscutting calcite carbonatite at the phlogopite deposit, Kovdor pluton, Kola Peninsula. Cancrinite (partly replaced with thomsonite-Ca), orthoclase, aegirine-augite, pectolite, magnesioarfvedsonite, golyshevite, and fluorapatite are associated minerals. Phosphoinnelite occurs as lath-shaped crystals up to 0.2 × 1 × 6 mm in size, which are combined typically in bunch-, sheaf-, and rosettelike segregations. The color is yellow-brown, with vitreous luster on crystal faces and greasy luster on broken surfaces. The mineral is transparent. The streak is pale yellowish. Phosphoinnelite is brittle, with perfect cleavage parallel to the {010} and good cleavage parallel to the {100}; the fracture is stepped. The Mohs hardness is 4.5 to 5. Density is 3.82 g/cm³ (meas.) and 3.92 g/cm³ (calc.). Phosphoinnelite is biaxial (+), α = 1.730, β = 1.745, and γ = 1.764, 2V (meas.) is close to 90°. Optical orientation is Z^c ∼ 5°. Chemical composition determined by electron microprobe is as follows (wt %): 6.06 Na₂O, 0.04 K₂O, 0.15 CaO, 0.99 SrO, 41.60 BaO, 0.64 MgO, 1.07 MnO, 1.55 Fe₂O₃, 0.27 Al₂O₃, 17.83 SiO₂, 16.88 TiO₂, 0.74 Nb₂O₅, 5.93 P₂O₅, 5.29 SO₃, 0.14 F, −O=F₂ = −0.06, total is 99.12. The empirical formula calculated on the basis of (Si,Al)₄O₁₄ is (Ba_3.59Sr_0.13K_0.01)_Σ3.73(Na_2.59Mg_0.21Ca_0.04)_Σ3.04(Ti_2.80Fe _0.26 ³⁺ Nb_0.07)_Σ3.13[(Si_3.93Al_0.07)_Σ4O₁₄(P_1.11S_0.87)_Σ1.98O_7.96](O_2.975F_0.10)_Σ3.075. The simplified formula is Ba₄Na₃Ti₃Si₄O₁₄(PO₄,SO₄)₂(O,F)₃. The mineral is triclinic, space group P or P1. The unit cell dimensions are a = 5.38, b = 7.10, c = 14.76 ?; α = 99.00°, β = 94.94°, γ = 90.14°; and V = 555 ?³, Z = 1. The strongest lines of the X-ray powder pattern [d, ? in (I)(hkl)] are: 14.5(100)(001), 3.455(40)(103), 3.382(35)(0 2), 2.921(35)(005), 2.810(40)(1 4), 2.683(90)(200, 01), 2.133(80)( 2), 2.059(40)(204, 1 3, 221), 1.772(30)(0 1, 1 7, 2 2, 2 3). The infrared spectrum is demonstrated. An admixture of P substituting S has been detected in the innelite samples from the Inagli pluton (South Yakutia, Russia). An innelite-phosphoinnelite series with a variable S/P ratio has been discovered. The type material of phosphoinnelite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? I.V. Pekov, N.V. Chukanov, I.M. Kulikova, D.I. Belakovsky, 2006, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2006, No. 3, pp. 52–60. Considered and recommended by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, May 9, 2005. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, July 4, 2005 (proposal 2005-022).     

Shlykovite KCa[Si4O9(OH)] · 3H2O and cryptophyllite K2Ca[Si4O10] · 5H2O, new mineral species from the Khibiny alkaline pluton, Kola Peninsula, Russia

New minerals, shlykovite and cryptophyllite, hydrous Ca and K phyllosilicates, have been identified in hyperalkaline pegmatite at Mount Rasvumchorr, Khibiny alkaline pluton, Kola Peninsula, Russia. They are the products of low-temperature hydrothermal activity and are associated with aegirine, potassium feldspar, nepheline, lamprophyllite, eudialyte, lomonosovite, lovozerite, tisinalite, shcherbakovite, shafranovskite, ershovite, and megacyclite. Shlykovite occurs as lamellae up to 0.02 × 0.02 × 0.5 mm in size or fibers up to 0.5 mm in length usually combined in aggregates up to 3 mm in size, crusts, and parallel-columnar veinlets. Cryptophyllite occurs as lamellae up to 0.02 × 0.1 × 0.2 mm in size intergrown with shlykovite being oriented parallel to {001} or chaotically arranged. Separate crystals of the new minerals are transparent and colorless; the aggregates are beige, brownish, light cream, and pale yellowish-grayish. The cleavage is parallel to (001) perfect. The Mohs hardness of shlykovite is 2.5–3. The calculated densities of shlykovite and cryptophyllite are 2.444 and 2.185 g/cm³, respectively. Both minerals are biaxial; shlykovite: 2V _meas = −60(20)°; cryptophyllite: 2V _meas > 70°. The refractive indices are: shlykovite: α = 1.500(3), β = 1.509(2), γ = 1.515(2); cryptophyllite: α = 1.520(2), β = 1.523(2), γ = 1.527(2). The chemical composition of shlykovite determined by an electron microprobe (H₂O determined from total deficiency) is as follows, wt %: 0.68 Na₂O, 11.03 K₂O, 13.70 CaO, 59.86 SiO₂, 14.73 H₂O; the total is 100.00. The empirical formula calculated on the basis of 13 O atoms (OH/H₂O calculated from the charge balance) is (K_0.96Na_0.09)_Σ1.05Ca_1.00Si_4.07O_9.32(OH)_0.68 · 3H₂O. The idealized formula is KCa[Si₄O₉(OH)] · 3H₂O. The chemical composition of cryptophyllite determined by an electron microprobe (H₂O determined from the total deficiency) is as follows, wt %: 1.12 Na₂O, 17.73 K₂O, 11.59 CaO, 0.08 Al₂O₃, 50.24 SiO₂, 19.24 H₂O, the total is 100.00. The empirical formula calculated on the basis of (Si,Al)₄(O,OH)₁₀ (OH/H₂O calculated from the charge balance) is (K_1.80Na_0.17)_Σ1.97Ca_0.99Al_0.01Si_3.99O_9.94(OH)_0.06 · 5.07H₂O. The idealized formula is K₂Ca[Si₄O₁₀] · 5H₂O. The crystal structures of both minerals were solved on single crystals using synchrotron radiation. Shlykovite is monoclinic; the space group is P2₁/n; a = 6.4897(4), b = 6.9969(5), c = 26.714(2)?, β = 94.597(8)°, V = 1209.12(15)?³, Z = 4. Cryptophyllite is monoclinic; the space group is P2₁/n; a = 6.4934(14), b = 6.9919(5), c = 32.087(3)?, β = 94.680(12)°, V= 1451.9(4)?, Z = 4. The strongest lines of the X-ray powder patterns (d, ?-I, [hkl] are: shlykovite 13.33–100[002], 6.67–76[004], 6.47–55[100], 3.469–45[021], 3.068–57[$ \bar 1 $ \bar 1 21], 3.042–45[121], 2.945–62[ 23], 2.912–90[025, 12, 211]; cryptophyllite 16.01–100[002], 7.98–24[004], 6.24–48[101], 3.228–22[$ \bar 1 $ \bar 1 09], 3.197–27[0.0.10], 2.995–47[122], 2.903–84[123, 204, $ \bar 1 $ \bar 1 24, 211], 2.623–20[028, 08, 126]. Shlykovite and cryptophyllite are members of new related structural types. Their structures are based on a two-layer packet consisting of tetrahedral Si layers linked with octahedral Ca chains. Mountainite, shlykovite and cryptophyllite could be combined into the mountainite structural family. Shlykovite is named in memory of Russian geologist V. G. Shlykov (1941–2007); the name cryptophyllite is from the Greek words meaning concealed and leaf that allude to its layered structure (phyllosilicate) in combination with a lamellar habit and intimate intergrowths with visually indistinguishable shlykovite. Type specimens of the minerals are deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow.     

Point defects and cation tracer diffusion in (Ti x Fe 1?x ) 3?δ O4 1. Non-stoichiometry and point defects

 The deviation from stoichiometry, δ, in spinel solid solutions of the type (Ti _x Fe _1−x )_3−δ O₄ with x=0.1, 0.2 and 0.25 was studied thermogravimetrically as a function of oxygen activity, a _O2, at 1100, 1200 and 1300 ^∘C. The experimental results, S-shaped curves for δ vs. log a_O2, are presented and discussed with regard to the type of point defects prevailing under different conditions in the deviation from stoichiometry. It is concluded that cation vacancies are the predominant point defects at high oxygen activities, while cation interstitials prevail at low oxygen activities. The temperature and composition dependencies of point defect concentrations are also discussed. Received: 1 October 1996 / Accepted: 15 September 2002 Acknowledgements The authors thank the US Department of Energy for support of this work under Grant no. DE-FGO2–88ER45357. This work made use of the Cornell Center of Materials Shared Experimental Facilities, supported through the National Science Foundation Materials Research Science and Engineering Centers program (DMR-0079992).     

Microscope-photometric methods for non-destructive Fe2+ – Fe3+ determination in chloritoids (Fe2+, Mn2+, Mg)2 (Al,Fe3+)4 Si2O10(OH)4

Six natural chloritoid crystals with Fe²⁺ and Fe³⁺ contents ranging from 4.15 to 12.81 and from 0.411 to 0.849g-atoms/l, respectively, as determined by means of microprobe and Mössbauer techniques, served as reference material to develop non-destructive microscope-spectrophotometric methods for quantitative Fe²⁺ – Fe³⁺ determinations in chloritoids from unpolarized spectra of (001) platelets. Fe²⁺ concentrations in g-atom/l can be obtained from [ [Fe³⁺]=C₁xD₁/t where D₁ = log₁₀(I_0/I at 28,000 cm^-1 and t=crystal thickness in cm; C₁ is a conttant that may be influenced somewhat by experimental conditions and is found to be 0.002289 with the experimental set-up used in this study. Fe²⁺ concentrations in g-atom/l can be obtained from [Fe²⁺]=C₁xD₁/D₁-C₃ with D₂=log₁₀(I₀/I) at 16,300 cm^?1 and constants C₄ = 45.36 and C₅ = 3.540. Due to the uncertainties in absorbance measurements, D₁ and D₂ and the thickness measurements, the accuracies are ±0.05 and ±0.15 g-atom/l for [Fe³⁺] and [Fe²⁺], respectively. The determinations may be carried out on chloritoid grains in normal thin sections with an areal resolution of ～10 μm.     

Fivegite K4Ca2[AlSi7O17(O2 ? xOHx)][(H2O)2 ? xOH]Cl: A new mineral species from the Khibiny alkaline pluton of the Kola Peninsula in Russia

A new mineral fivegite has been identified in a high-potassium hyperalkaline pegmatite at Mt. Rasvumchorr in the Khibiny alkaline complex of the Kola Peninsula in Russia. This mineral is a product of the hydrothermal alteration of delhayelite (homoaxial pseudomorphs after its crystals up to 2 × 3 × 10 cm in size). Hydrodelhayelite, pectolite, and kalborsite are products of fivegite alteration. The associated minerals are aegirine, potassic feldspar, nepheline, sodalite, magnesiumastrophyllite, lamprophyllite, lomonosovite, shcherbakovite, natisite, lovozerite, tisinalite, ershovite, megacyclite, shlykovite, cryptophyllite, etc. Areas of pure unaltered fivegite are up to 2 mm in width. The mineral is transparent and colorless; its luster is vitreous to pearly. Its Cleavage is perfect (100) and distinct (010). Its Mohs hardness is 4, D(meas) = 2.42(2), and D(calc) = 2.449 g/cm³. Fivegite is optically biaxial positive: α 1.540(1), β 1.542(2), γ 1.544(2), and 2V(meas) 60(10)°. Its orientation is X = a, y = c, and Z = b. Its IR spectrum is given. Its chemical composition (wt %; electron microprobe, H₂O determined by selective sorption) is as follows: 1.44 Na₂O, 19.56 K₂O, 14.01 CaO, 0.13 SrO, 0.03 MnO, 0.14 Fe₂O₃, 6.12 Al₂O₃, 50.68 SiO₂, 0.15 SO₃, 0.14 F, 3.52 Cl, 4.59 H₂O; −O = −0.85(Cl,F)2; total 99.66. The empirical formula based on (Si + Al + Fe) = 8 is H_4.22K_3.44Na_0.39Ca_2.07Sr_0.01Fe_0.01Al_1.00Si_6.99O_21.15F_0.06Cl_0.82(SO₄)_0.02. The simplified formula is K₄Ca₂[AlSi₇O₁₇(O_{2 − x} OH _x ][(H₂O)_{2 − x} OH _x ]Cl (X = 0−2). Fivegite is orthorhombic: Pm2₁ n, a = 24.335(2), b = 7.0375(5), c = 6.5400(6) ?, V = 1120.0(2) ?³, and Z = 2. The strongest reflections of the X-ray powder pattern are as follows (d, ?, (I, %), [hkl]): 3.517(38) [020], 3.239(28) [102], 3.072(100) [121, 701], 3.040(46) [420, 800, 302], 2.943 (47) [112], 2.983(53) [121], 2.880 (24) [212, 402], 1.759(30) [040, 12.2.0]. The crystal structure was studied using a single crystal: R _hkl = 0.0585. The base of fivegite structure is delhayelite-like two-layer terahedral blocks [(Al,Si)₄Si₁₂O₃₄(O_{4 − x} OH _x )] linked by Ca octahedral chains. K⁺ and Cl⁻ are localized in zeolite-like channels within the terahedral blocks, whereas H₂O and OH occur between the blocks. The mineral is named in memory of the Russian geological and mining engineer Mikhail Pavlovich Fiveg (1899–1986), the pioneering explorer of the Khibiny apatite deposits. The type specimen is deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow. The series of transformations is discussed: delhayelite K₄Na₂Ca₂[AlSi₇O₁₉]F₂Cl—fivegite K₄Ca₂[AlSi₇O₁₇(O_{2 − x} OH _x ]Cl—hydrodelhayelite KCa₂[AlSi₇O₁₇(OH)₂](H₂O)_{6 − x} .     

Eurekadumpite, (Cu,Zn)16(TeO3)2(AsO4)3Cl(OH)18·7H2O, a new supergene mineral species

A new mineral eurekadumpite found at the Centennial Eureka Mine in the Tintic district of Juab County in Utah in the United States occurs in the oxidation zone along with quartz, macalpineite, malachite, Zn-bearing olivenite, goethite, and Mn oxides. Eurekadumpite forms spherulites or rosettes up to 1 mm in size and their clusters and crusts up to 1.5 cm² in cavities. Its individuals are divergent and extremely thin (up to 0.5 mm across and less than 1 μm thick) hexagonal or roundish leaflets. The mineral is deep blue-green or turquoise-colored. Its streaks are light turquoise-colored. Its luster is satiny in aggregates and pearly on individual flakes. Its cleavage is (010) perfect and micalike. Its flakes are flexible but inelastic. Its Mohs hardness is 2.5–3.0, and D(meas) = 3.76(2) and D(calc) = 3.826 g/cm³. The mineral is optically biaxial negative, and α = 1.69(1), β ∼ γ = 1.775(5), and 2V _meas = 10(5)°. Its pleochroism is strong: Y = Z = deep blue-green, and X = light turquoise-colored. Its orientation is X = b. The wavenumbers of the bands in the IR spectrum (cm⁻¹; the strong lines are underlined, and w denotes the weak bands) are 3400, 2990, 1980w, 1628, 1373w, 1077, 1010, 860, 825, 803, 721w, 668, 622, 528, 461. The IR spectrum shows the occurrence of the tellurite (Te⁴⁺,O₃)²⁻ and arsenate (As⁵⁺,O₄)³⁻ anionic groups and H₂O molecules; Cu and Zn cations are combined with OH⁻ groups. The chemical composition of eurekadumpite is as follows (wt %, average of 14 electron-microprobe analyses; H₂O determined using the Alimarin method): 0.04 FeO, 36.07 CuO, 20.92 ZnO, 14.02 TeO₂, 14.97 As₂O₅, 1.45 Cl, 13.1 H₂O, O = Cl₂ −0.33, total 100.24. The empirical formula based on 2 Te atoms is (Cu_10.32Zn_5.85Fe_0.01)_Σ16.18(TeO₃)₂(AsO₄)_2.97[Cl_0.93(OH)_0.07]_Σ1(OH)_18.45 · 7.29H₂O. The idealized formula is (Cu,Zn)₁₆(TeO₃)₂(AsO₄)₃Cl(OH)₁₈ · 7H₂O. Eurekadumpite is monoclinic (pseudohexagonal), and the most probable space groups are P2/m, P2, or Pm. The unit-cell parameters refined from the powder X-ray data are as follows: a = 8.28(3), b = 18.97(2), c = 7.38(2) ?, β = 121.3(6)°, V = 990(6) ?³, and Z = 1. The strongest reflections of the X-ray powder pattern (d, ? (I) [hkl]) are as follows: 18.92(100) [010], 9.45(19) [020], 4.111(13) [[`2]\bar 2 01], 3.777(24) [050, [`2]\bar 2 21, 041], 2.692(15) [[`3]\bar 3 11, 151, [`3]\bar 3 02], 2.524(41)[170, [`2]\bar 2 52, [`1]\bar 1 71], 1.558(22) [[`4]\bar 4 82, [`3]\bar 3 .10.1, 024]. The name of the mineral means, firstly, that it was found in specimens from dumps of the Centennial Eureka Mine. In addition, it could mean found in a dump (the Greek word eureka means I have found it). There is an allusion to the great role that dumps of abandoned mines have played in the discovery of new minerals. Type specimens are deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences in Moscow, at the Smithsonian National Museum of Natural History in Washington, and at the American Museum of Natural History in New York.     

Schüllerite, Ba2Na(Mn,Ca)(Fe3+,Mg,Fe2+)2Ti2(Si2O7)2(O,F)4, a new mineral species from the Eifel volcanic district, Germany

A new heterophyllosilicate mineral schüllerite was found in the L?hley basalt quarry in the Eifel volcanic region, Germany, as a member of the late mineral assemblage comprising nepheline, leucite, augite, phlogopite, magnetite, titanite, fresnoite, barytolamprophyllite, fluorapatite, perovskite, and pyrochlore. Flattened brown crystals of schüllerite up to 0.5 × 1 × 2 mm in size and their aggregates occur in miarolic cavities of alkali basalt. The mineral is brittle, with a Mohs hardness 3–4 and perfect cleavage parallel to (001). D _calc = 3.974 g/cm³. Its IR spectrum is individual and does not contain bands of OH⁻, CO₃²⁻ or H₂O. Schüllerite is biaxial (−), α = 1.756(3), β = 1.773(4), γ = 1.780(4), 2V _meas = 40(20)°. Dispersion is weak, r < ν. Pleochroism is medium X > Y > Z, brown to dark brown. Chemical composition (electron microprobe, mean of five-point analyses, Fe²⁺/Fe³⁺ ratio determined by the X-ray emission spectroscopic data, wt %): 3.55 Na₂O, 0.55 K₂O, 3.89 MgO, 2.62 CaO, 1.99 ArO, 28.09 BaO, 3.43 FeO, 8.89 Fe₂O₃, 1.33 Al₂O₃, 11.17 TiO₂, 2.45 Nb₂O₅, 26.12 SiO₂, 2.12 F, −0.89 -O=F₂, 98.98 in total. The empirical formula is (Ba_1.68Sr_0.18K_0.11Na_1.05Ca_0.43Mn_0.47Mg_0.88Fe_0.44²⁺Fe_1.02³⁺Ti_1.28Nb_0.17Al_0.24)_Σ7.95Si_3.98O_16.98F_1.02. The crystal structure was refined on a single crystal. Schüllerite is triclinic, space group P1, unit cell parameters: a = 5.4027(1), b = 7.066(4), c = 10.2178(1)?, α = 99.816(1), β = 99.624(1), γ = 90.084(1)°, V = 378.75(2) ?³, Z = 1. The strongest lines of the X-ray powder diffraction pattern [d, ?, (I, %)]: 9.96(29), 3.308(45), 3.203(29), 2.867(29), 2.791(100), 2.664(46), 2.609(36), 2.144(52). The mineral was named in honor of Willi Schüller (born 1953), an enthusiastic, prominent amateur mineral collector, and a specialist in the mineralogy of Eifel. Type specimens have been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, registration no. 3995/1,2.     

H T -XRD study of synthetic ferrian magnesian spodumene: the effect of site dimension on the P 21/ c → C 2/ c phase transition

 Ferrian magnesian spodumene was synthesized in the MLFSH system at P=0.4 GPa, T=700 °C, fO₂=NNO+2.3. The space group at room T is P2₁/c [a=9.638(3) ?, b=8.709(2) ?, c=5.258(2) ?, β=109.83(3)^∘, V=415.2 ?³]. The structure is topologically equivalent to that of ferrian spodumene, LiFeSi₂O₆, and has two symmetrically independent tetrahedral chains, A and B, and two independent octahedral sites, M1 and M2. The crystal-chemical composition was determined combining EMP, SIMS and single-crystal XRD analysis, yielding ^M2(Li_0.85Mg_0.09Fe²⁺ _0.06) ^M1(Fe³⁺ _0.85Mg_0.15)Si₂O₆. Li is ordered at the M2 site and Fe³⁺ is ordered at the M1 site, whereas Mg (and Fe²⁺) distribute over both octahedral sites. Structure refinements done at different temperatures (25, 70, 95, 125, 150 and 200 °C) allowed characterization of a reversible displacive P2₁/c→C2/c transition at 106 °C. Previous HT-XRD studies of Li-clinopyroxenes had shown that the transition temperature is inversely related to the size of the M1 cation. For the crystal of this work, the aggregate ionic radius at M1 is longer than that of ferrian spodumene, for which the transition temperature is −44 °C. The higher transition temperature observed can only be explained on the basis of the shorter aggregate radius at the M2 site (due to the presence of Mg substituting after Li), in keeping with the results obtained for ferromagnesian P2₁/c pyroxenes. The effects of all the chemical substitutions must be considered when modelling transition temperatures and thermodynamic behaviour in clinopyroxenes. Received: 7 May 2002 / Accepted: 23 October 2002     

Batiferrite, Ba[Ti2Fe10]O19, a new ferrimagnetic magnetoplumbite-type mineral from the Quaternary volcanic rocks of the western Eifel area, Germany

Summary Batiferrite, ideally Ba[Ti₂Fe₁₀]O₁₉, was found in the Quaternary volcanic rocks near üdersdorf, Graulai, and Altburg, western Eifel area, Germany. The new mineral typically occurs as euhedral platy grains in cavities of melilite- and leucite-nephelinite basalts. Associated minerals are hematite, magnetite, titanite, g?tzenite, clinopyroxene, nepheline, and biotite. It exhibits a hexagonal tabular habit flattened on {0001}, diameter 0.5–1 mm, thickness 20–125 μm, and {10&1macr;3}, {10&1macr;0} as observable forms. The mineral is opaque, of black color with submetallic lustre, and shows a ferrimagnetic behavior. VHN₅₀ is 793 with a range of 710–841 from ten indentations. The quantitative reflectance measurements of R_o/R_e on oriented grains in air and oil immersion, respectively, are [%]: for 470 nm 22.1/20.1 and 8.4/7.1, for 546 nm 21.0/19.4 and 7.8/6.6, for 589 nm 20.2/18.8 and 7.4/6.3, and for 650 nm 19.3/18.3 and 6.8/5.9. The bireflectance is distinct (air) to weak (oil), and parallel (0001) a moderate anisotropy with straight extinction can be observed. Typical microprobe analyses give [wt%] K₂O 0.28–0.33, Na₂O 0.17–0.20, SrO 0.46–0.55, BaO 11.80–12.17, MgO 1.27–1.47, Al₂O₃ 0.31–0.33, TiO₂ 13.11–13.63, MnO 2.38–2.57, Fe₂O₃ 61.36–63.12, FeO 5.49–5.86 (Fe³⁺/Fe²⁺ calculated for charge compensation), which is equivalent to (Ba_0.84Na_0.06K_0.06Sr_0.05)_1.01(Fe_8.48 ³⁺Fe_0.86 ²⁺Ti_1.82Mg_0.37Mn_0.37Al_0.06)_11.96O₁₉ as the average composition based on 19 oxygen atoms. Batiferrite is a magnetoplumbite-type mineral with hexagonal symmetry, space group P6 ₃ /mmc (no. 194), a = 5.909(1) ?, c = 23.369(4) ?, V = 706.6(2) ?³, Z = 2, and a calculated density of 5.016 gcm⁻³. The structure was refined to R1 = 0.031 for 278 unique reflections with F_o ² > 4σ (F_o ²) and R1 = 0.079 for all 452 unique observations using single crystal X-ray data. The strongest reflections of the X-ray powder diffraction pattern are [d _obs, I/I_o, (hkl)]: 2.631, 100, (114); 2.799, 80, (107); 1.478, 70, (220); 2.429, 60, (203); 1.672, 50, (217). The new mineral is comparable to the other Ba containing magnetoplumbite-type minerals haggertyite and hawthorneite, the iron content, however, is much higher and in the range of magnetoplumbite. The large cation site (A) is dominated by Ba, and four of the five remaining crystallographic cation sites in the structure are dominated by Fe (M1, 2, 3, 5), the octahedrally coordinated M4-site is dominated by Ti. No oxygen vacancy on the O3-site like in plumboferrite can be observed. Batiferrite is named for its main chemical composition and the relationship to the M-type hexaferrites (polytype 5H).

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Zusammenfassung Batiferrit, ein neues ferrimagnetisches Mineral des Magnetoplumbit-Typs aus den quart?ren Vulkaniten der West-Eifel, Deutschland Das neue Mineral Batiferrite, mit der Idealformel Ba[Ti₂Fe₁₀]O₁₉, wurde an drei Fundpunkten in den Quart?ren Vulkangesteinen der westlichen Eifel, Deutschland, in der N?he von üdersdorf, Graulai und Altburg gefunden. Das neue Mineral tritt typischerweise bl?ttchenf?rmig in kleinen Hohlr?umen von Melilith- und Leucit-Nephelininit Basalten auf. Vergesellschaftete Minerale sind H?matit, Magnetit, Titanit, G?tzenit, Klinopyroxen, Nephelin und Biotit. Der Habitus ist hexagonal tafelig nach {0001}, mit einem Durchmesser von 0.5–1 mm und einer Dicke von 20–125 μm, zus?tzlich k?nnen die Formen {10&1macr;3} und {10&1macr;0} beobachtet werden. Das Mineral ist opak, hat eine schwarze Farbe mit einem leicht metallischen Glanz, und ist ferromagnetisch. Die H?rte VHN₅₀ ist 793 mit einem Bereich von 710–841 aus 10 Eindruckbestimmungen. Die quantitativen Reflexionsmessungen von R_o/R_e an orientierten K?rnern in Luft beziehungsweise ?limmersion, ergaben [%]: für 470 nm 22.1/20.1 und 8.4/7.1, für 546 nm 21.0/19.4 und 7.8/6.6, für 589 nm 20.2/18.8 und 7.4/6.3, und für 650 nm 19.3/18.3 und 6.8/5.9. Die Bireflexion ist deutlich (Luft) bis schwach (?l) und parallel (0001) kann eine mittlere Anisotropie mit gerader Ausl?schung beobachtet werden. Eine typische Mikrosondenanalyse ergibt [wt%] K₂O 0.28–0.33, Na₂O 0.17–0.20, SrO 0.46–0.55, BaO 11.80–12.17, MgO 1.27–1.47, Al₂O₃ 0.31–0.33, TiO₂ 13.11–13.63, MnO 2.38–2.57, Fe₂O₃ 61.36–63.12, FeO 5.49–5.86 (Fe³⁺/Fe²⁺ berechnet zum Ladungsausgleich), die mittlere chemische Formel auf der Basis von 19 Sauerstoffatomen lautet (Ba_0.84Na_0.06K_0.06Sr_0.05)_1.01 (Fe_8.48 ³⁺Fe_0.86 ²⁺Ti_1.82Mg_0.37Mn_0.37Al_0.06)_11.96O ₁₉. Batiferrit ist ein Mineral der Magnetoplumbitgruppe, hat hexagonale Symmetrie mit der Raumgruppe P6₃/mmc (Nr. 194), a = 5.909(1) ?, c = 23.369(4) ?, V = 706.6(2) ?³, Z = 2, und einer berechneten Dichte von 5.016 gcm⁻³. Die Struktur wurde aus Einkristall-R?ntgendaten bis zu einem R1-Wert von 0.031 für 278 F_o ² > 4σ(F_o ²), und einem R1-Wert von 0.079 für alle 452 F_o ² verfeinert. Die st?rksten Beugungsreflexe der Pulver-R?ntgendaten sind [d_obs, I/I_o, (hkl)]: 2.631, 100, (114); 2.799, 80, (107); 1.478, 70, (220); 2.429, 60, (203); 1.672, 50, (217). Das neue Mineral weist deutliche ?hnlichkeiten zu den anderen beiden Ba-reichen Mineralen Haggertyit und Hawthorneit der Magnetoplumbit-Gruppe auf, jedoch ist der Eisengehalt wesentlich h?her und im Bereich des Minerals Magnetoplumbit. Der gro?e Kationenplatz (A) ist von Barium dominiert, vier (M1, 2, 3, 5) der restlichen fünf kristallographischen Kationenpl?tze in der Struktur sind fast ausschlie?lich mit Fe, die oktaedrisch koordinierte M4-Position ist überwiegend mit Ti besetzt. An der O3-Position konnte kein Sauerstoffdefizit wie in Plumboferrit festgestellt werden. Batiferrit ist nach seiner chemischen Beschaffenheit und nach seiner Zugeh?hrigkeit zu den M-Typ Hexaferriten (Polytyp 5H) benannt.

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Received December 14, 1999; accepted March 2, 2000     

Variation of infrared absorption spectra in the system Bi2Al4−x Fe x O9 (x = 0–4), structurally related to mullite

The crystal structure of Bi₂Al_4−x Fe _x O₉ compounds (x = 0–4) has striking similarities with the crystal structure of mullite. A complete substitution of Al by Fe³⁺ in both octahedral and tetrahedral sites is a particular structural feature. The infrared (IR) spectra of the Bi₂M₄O₉ compounds (M = Al, Fe³⁺) are characterised by three band groups with band maxima in the 900–800, 800–600 and 600–400 cm⁻¹ region. Based on the spectroscopic results obtained from mullite-type phases, the present study focuses on the composition-dependent analysis of the 900–800 cm⁻¹ band group, which is assigned to Al(Fe³⁺)–O stretching vibrations of the corner-sharing MO₄ tetrahedra. The Bi₂Al₄O₉ and Bi₂Fe₄O₉ endmembers display single bands with maxima centred at 922 and 812 cm⁻¹, respectively. Intermediate Bi₂Al_4−x Fe _x O₉ compounds exhibit a distinct splitting into three relatively sharp bands, which is interpreted in terms of ordering effects within the tetrahedral pairs. Thereby the high-energy component band of the band triplet relates to Al–O–Al conjunctions and the low-energy component band to Fe–O–Fe conjunctions. The intermediate band is assigned to stretching vibrations of Al–O–Fe or Fe–O–Al configurations of the corner-sharing tetrahedral pairs. Bands in the 800–600 cm⁻¹ range are assigned to low-energy stretching vibrations of the MO₄ tetrahedra and to M–O–M bending vibrations of the tetrahedral pairs. Absorptions in the 600–400 cm⁻¹ range are essentially determined by M–O stretching modes of the M cations in octahedral coordination.     

Thermochemistry of yavapaiite KFe(SO4)2: Formation and decomposition

Yavapaiite, KFe(SO₄)₂, is a rare mineral in nature, but its structure is considered as a reference for many synthetic compounds in the alum supergroup. Several authors mention the formation of yavapaiite by heating potassium jarosite above ca. 400°C. To understand the thermal decomposition of jarosite, thermodynamic data for phases in the K-Fe-S-O-(H) system, including yavapaiite, are needed. A synthetic sample of yavapaiite was characterized in this work by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal analysis. Based on X-ray diffraction pattern refinement, the unit cell dimensions for this sample were found to be a = 8.152 ± 0.001 Å, b = 5.151 ± 0.001 Å, c = 7.875 ± 0.001 Å, and β = 94.80°. Thermal decomposition indicates that the final breakdown of the yavapaiite structure takes place at 700°C (first major endothermic peak), but the decomposition starts earlier, around 500°C. The enthalpy of formation from the elements of yavapaiite, KFe(SO₄)₂, ΔH°_f = −2042.8 ± 6.2 kJ/mol, was determined by high-temperature oxide melt solution calorimetry. Using literature data for hematite, corundum, and Fe/Al sulfates, the standard entropy and Gibbs free energy of formation of yavapaiite at 25°C (298 K) were calculated as S°(yavapaiite) = 224.7 ± 2.0 J.mol⁻¹.K⁻¹ and ΔG°_f = −1818.8 ± 6.4 kJ/mol. The equilibrium decomposition curve for the reaction jarosite = yavapaiite + Fe₂O₃ + H₂O has been calculated, at pH₂O = 1 atm, the phase boundary lies at 219 ± 2°C.     

Solid solutions of (Mg,Fe<Superscript>2+</Superscript>)-cordierite: Synthesis,water content,and magnetic properties

The dependence of water concentration in synthetic (Mg, Fe²⁺)-cordierite on the composition of the solid solution was examined in experiments that lasted for 10 days at = 200–230 MPa, t = 600–700°C, and oxygen fugacity corresponding to the Fe-FeO buffer. Mass spectrometric data indicate that the dependence of water concentration in cordierite on its Fe mole fraction Fe²⁺/(Fe²⁺ + Mg) has maxima at compositions with F = 0.2–0.3. IR diffuse reflectance spectroscopic data and data on the structural setting of H₂O molecules in the structural channels of alkali-free (Mg, Fe²⁺)-cordierite indicate that the H-H vector of some H₂O molecules (H₂O-II) is perpendicular to [001] of the crystal. The dependence of the magnetic properties of synthetic (Mg, Fe²⁺)-cordierite was studied by static magnetization technique at 5–300 K in an external magnetic field up to 20 kOe in strength.     

K-H3OFe3(SO4)2(OH)6铁矾的XRD研究

根据X射线衍射(XRD)分析发现: A Fe₃(SO₄)₂(OH)₆(A=K⁺、H₃O⁺)系列铁钒的XRD数据十分相近,难以用XRD区别,需通过能谱(EDS)辅助分析,才能区分此类铁矾。另外,此类铁矾的003和107面网间距d随K⁺含量增大而增大,且呈一元三次方程的关系;而033和220面网间距d随K⁺含量增大而减小,呈一元二次方程的关系。对该现象从铁矾晶体结构方面进行解释:K⁺、H₃O⁺离子位于较大空隙中,且沿着Z轴方向排列,当K⁺、H₃O⁺离子之间相互替换时,会导致该铁矾晶体结构在Z轴方向有较明显的变化。     

The stability of primary alluaudites in granitic pegmatites: an experimental investigation of the Na2(Mn2−2x Fe1+2x )(PO4)3 system

In order to assess the geothermometric potential of the Na₂(Mn_2−2x Fe_1+2x )(PO₄)₃ system (x = 0–1), which represents the compositions of natural weakly oxidized alluaudites, we performed hydrothermal experiments between 400 and 800°C, at 1 kbar, under an oxygen fugacity (f(O₂)) controlled by the Ni–NiO (NNO), Fe₂O₃–Fe₃O₄ (HM), Cu₂O–CuO (CT), and Fe–Fe₃O₄ (MI) buffers. When f(O₂) is controlled by NNO, single-phase alluaudites crystallize at 400 and 500°C, whereas the association alluaudite + marićite appears between 500 and 700°C. The limit between these two fields corresponds to the maximum temperature that can be reached by alluaudites in granitic pegmatites, because marićite has never been observed in these geological environments. Because alluaudites are very sensitive to variations of oxygen fugacity, the field of hagendorfite, Na₂MnFe²⁺Fe³⁺(PO₄)₃, has been positioned in the f(O₂)–T diagram, and provides a tool that can be used to estimate the oxygen fugacity conditions that prevailed in granitic pegmatites during the crystallization of this phosphate.     

Cuprokalininite, CuCr2S4, a new sulfospinel from metamorphic rocks of the Sludyanka Complex, South Baikal region

Cuprokalininite as an accessory mineral has been found in Cr-V-bearing quartz-diopside metamorphic rock of the Sludyanka Complex, South Baikal region, Russia. This mineral is named as Cu analogue of kalininite (ZnCr₂S₄), is associated with quartz, Cr-V-bearing tremolite and mica, calcite, diopside-kosmochlor, goldmanite-uvarovite, dravite-chromdravite, Cr-V spinellide, karelianite-eskolaite, V-bearing titanite, pyrite, and plagioclase. Cuprokalininite forms euhedral microcrystals up to 0.05–0.20 mm in size, of octahedral and cuboctahedral habit with faces o {111} and a {100}, and polysynthetic and simple twinning along the {111}. Cleavage and parting were not observed. The mineral is black with a dark bronze tint, black streak, and metallic luster. The microhardness (VHN) is 356–458 (loadings are 20 and 30 g), 396 kgf/mm², on average. The Mohs hardness is 4.5–5.0, d _calc = 4.16(2). In reflected light, the mineral is pale-cream-colored, without anisotropy; reflectance values (λ, nm-R, %): 400-34.3, 420-34.1, 440-33.9, 460-33.7, 480-33.5, 500-33.2, 520-33.0, 540-32.8, 560-32.3, 580-32.2, 600-31.9, 620-31.6, 640-31.2, 660-30.9, 680-30.6, 700-30.4. Cubic, space group Fd [`3]\bar 3 m, Z = 8; unit cell parameter a = 9.814(2) ?, V = 945.2(4) ?³. The strongest lines of the X-ray powder diffraction pattern [d, ? (I) (hkl)]: 3.44 (6)(220), 2.94 (10)(311), 2.44 (6)(400), 1.884 (9)(511, 333), 1.731 (10)(440), 1.133 (6)(751, 555), 1.098 (6)(840), 1.030 (6)(931), 1.002 (10)(844). Chemical composition (mean of 202 microprobe analyses of 11 grains, wt %): Cu 21.03, Fe 0.47, Zn 0.17, Cr 29.01, V 5.85, As 0.21, Sb 0.08, S 43.25; the total is 100.07. The empirical formula calculated on the basis of seven ions is (Cu_0.98Fe_0.02Zn_0.01)_1.01(Cr_1.65V_0.34As_0.01)_2.00S_3.99. The type material has been deposited at the Fersman Mineralogical Museum of the Russian Academy of Sciences, Moscow, Russia.     

Ferric-ferrous ratios,H2O contents and D/H ratios of phlogopite and biotite from lavas of different tectonic regimes

 Complete chemical analyses, including ferric and ferrous iron, H₂O contents and δD values for 16 phlogopite and biotite and 2 hornblende separates are presented. Samples were obtained from volcanic rocks from four localities: (1) phlogopite phenocrysts from minette lavas from the western Mexico continental arc, (2) biotite and hornblende phenocrysts from andesite lavas from Mono Basin, California, (3) phlogopite and biotite from clinopyroxenite nodules entrained in potassic lavas from the East African Rift, Uganda, and (4) phlogopite phenocrysts from a wyomingite lava in the Leucite Hills, Wyoming. The Fe₂O₃ contents in the micas range from 0.8 to 10.5 wt%, corresponding to 0.09 to 1.15 Fe³⁺ per formula unit (pfu). Water contents vary from 1.6 to 3.0 wt%, corresponding to 1.58 to 3.04 OH pfu, significantly less than would be expected for a site fully occupied by hydroxyl. Cation- and anion-based normalization procedures provide accurate mineral formulae with respect to most cations and anions, but are unable to generate accurate estimates of Fe³⁺/Fe^T, and overestimate OH at the expense of O on the hydroxyl site. These inaccuracies are present despite acceptable adjusted totals and stoichiometric calculated site occupancies. The phlogopite and biotite phenocrysts in arc-related lavas from western Mexico and eastern California have the highest Fe³⁺/Fe^T ratios (56–87%), reflecting high magmatic oxygen fugacities (ΔNNO = +2 to +5), in contrast to those from Uganda (25–40%) and the Leucite Hills (23%). There is no correlation between the OH content and the Fe³⁺/Fe^T ratio in the micas. Values of KMg/Fe²⁺D (± 2σ errors) were calculated for three phlogopite-olivine pairs (0.12 ± 0.12, 0.26 ± 0.14, 0.09 ± 0.12), two biotite-hornblende pairs (0.73 ± 0.08 and 1.22 ± 0.10) and a single phlogopite-augite pair (1.15 ± 0.12). Values of KF/OHD for two biotite and hornblende pairs could not be determined without significant error because of the extremely low F contents (< 0.2 wt%) of the four phases. The δD values obtained in this study encompass a large range (−137 to −43‰). The phlogopite and biotite separates from Uganda have δD values of −70 to −49‰, which overlap those believed to represent “primary” mantle. There is a larger range in δD values (−137 to −43‰) for phlogopite phenocrysts from western Mexico minette lavas, although their range in δ¹⁸O values (5.2–6.2‰) is consistent with “normal” mantle. It is unlikely, therefore, that the variable δD values reflect heterogeneity in the mantle source region of the minette magmas. Nor can the extremely low δD values reflect degassing of H₂ or H₂O since almost 100% loss of dissolved water in the magma is required, an unrealistic scenario given the stability of the hydrous phenocrysts. The very low δD values of the Mascota minette phlogopites require that the hydrogen be introduced from an external source (e.g., meteoric water). Whatever the process responsible for the observed hydrogen isotope composition, it had no effect on the δ¹⁸O value, f _{O 2}, a _{H 2O} or bulk composition of the host magmas. Received: 5 January 1995 / Accepted: 19 March 1996     

La sénégalite,Al2 (PO4) (OH)3 · H2O,un nouveau minéral

Senegalite is orthorhombic, mm2, a:b:c:=1.296:1:1.007; $\text{a}{}_0\text{=9.673,}\text{b}{}_0\text{=7.596,}\text{c}{}_0\text{=7.668}\text{A}\text{?}$, Z=4, G_calc=2551; space group Pna2. The strongest lines in the powder pattern are: 5.41(7); 4.089(9); 3.834(10); 3.610(8); 2.990(9); 2.348(8); 2.070(7) 1.929(7); 1.505(7) Å. The chemical analysis: Al₂O₃ ? 46.23; Fe₂O₃ ? 0.28; P₂O₅ ? 31.85 H₂O ? 21.00; sum 99.34, gives a formula Al₂(PO₄)(OH)₃ · H₂O. Colourless optically biaxial positive, n_S: α=1.562, β=1.566, γ=1.587, plane of optical axies (001), Z=a, Y=c; 2V=53°, weak dispersion r > v. Measured density 2.552. The DTA curve shows endothermic reactions at 250, 370 and 440°C corresponding to the dehydration of mineral. Infrared spectrum indicates the presence of OH and H₂O groups. Found in oxidation zone of Kouroudiako iron deposit, Senegal, associated with turquoise, augelite, wavellite and crandallite.     

The Kinetics of the Interaction Between Iron(III)-Ethylenediaminetetraacetate and Peroxynitrite

The kinetics of the formation of the purple-colored species between Fe^III-EDTA and peroxynitrite were studied as a function of pH (10.4–12.3) at 22°C in aqueous solutions using a stopped-flow technique. A purple-colored species was immediately formed upon mixing, which had an absorbance maximum at 520 nm. The increase in absorbance with time could be fit empirically by a power function with two parameters a and b. The power equation determined was absorbance = a*t ^b , where a increased linearly with pH and the concentration of peroxynitrite, while b almost remained constant with a value of ~0.25. The molar extinction coefficient ε_520 nm for the colored species was determined as 13 M⁻¹cm⁻¹, which is much lower than ε_520 nm = 520 M⁻¹ cm⁻¹ for the [Fe^III(EDTA)O₂]³⁻, a purple species observed in the Fe^III–EDTA–H₂O₂ system. The results of kinetics and spectral measurements of the present study are briefly discussed and compared with those of the reaction between Fe(III)-EDTA and hydrogen peroxide.