Dan Holtstam

Crystal chemistry of REEXO4 compounds (X = P, As, V). II. Review of REEXO4 compounds and their stability fields

A comprehensive critical review of the phase fields, metastable modifications, solid solution ranges and phase transitions of monazite- and zircon-type REE X O 4 ( X = P, As, V) compounds is given. Monazite-type REEPO 4 compounds are stable for REE = La to Gd and metastable for Tb to Ho; zircon-type members exist for REE = Gd to Lu, and Y, Sc. REEAsO 4 compounds with monazite-type structure exist for REE = La to Nd, while zircon-type compounds are known for REE = Pm to Lu, and Y, Sc; no metastable arsenate members are known. The only stable monazite-type REEVO 4 is LaVO 4 , but metastable members are known for REE = Ce to Nd. Zircon-type REEVO 4 compounds are stable for REE = Ce to Lu, and Y, Sc, and metastable for REE = La. Solid solution series are complete only if minor size differences exist between REE 3+ or X 5+ cations in respective end-members. Phase transitions occur under pressure (zircon → (monazite →) scheelite) and at very low temperatures. The evaluation of the metastable phase fields and of naturally occurring members suggests that metastable modifications of REE X O 4 compounds can occur in nature under certain conditions (formation at temperatures

Västmanlandite-(Ce) - a new lanthanide- and F-bearing sorosilicate mineral from Västmanland, Sweden: description, crystal structure, and relation to gatelite-(Ce)

Vastmanlandite-(Ce), ideally (Ce,La) 3 CaAl 2 Mg 2 [Si 2 O 7 ][SiO 4 ] 3 F(OH) 2 , is a new mineral species from the Vastmanland county, Bergslagen region, Sweden. Together with more Fe-rich, F-poor members, it forms solid solutions that are important for lanthanide sequestration in the Bastnas-type skarn deposits in Vastmanland. At the type locality (Malmkarra, Norberg district) it occurs as anhedral grains 0.2–3 mm across, in association with fluorbritholite-(Ce), tremolite, a serpentine mineral, magnetite, dollaseite-(Ce) and dolomite. The mineral is allanite-like in appearance; it is dark brown, translucent, with vitreous luster, and has good cleavage parallel to {001}, uneven to conchoidal fracture, and a yellowish gray streak; D calc = 4.51(2) g·cm −3 and Mohs hardness ≈ 6. Optically it is biaxial (-), with α = 1.781 (4), β calc = 1.792, γ = 1.810(4) and 2V α = 75(5)°. Chemical analysis by electron-microprobe and 57 Fe Mossbauer spectroscopy yield: La 2 O 3 13.65, Ce 2 O 3 23.90, Pr 2 O 3 2.07, Nd 2 O 3 6.28, Sm 2 O 3 0.42, Gd 2 O 3 0.15, Y 2 O 3 0.18, CaO 4.65, FeO 1.14, Fe 2 O 3 2.69, MgO 5.51, Al 2 O 3 8.58, TiO 2 0.04, P 2 O 5 0.05, SiO 2 26.61, F 1.06, H 2 O calc 1.61, O ≡ F −0.45, sum 98.14. Vastmanlandite-(Ce) is monoclinic, P2 1 / m , with a = 8.939(1), b = 5.706(1), c = 15.855(2) A, β = 94.58(1)°, V = 806.1(2) A 3 , and Z = 2 (single-crystal data). The eight strongest lines in the X-ray powder diffraction pattern are [ d (in A) ( I/I 0 )( hkl )]: 15.81(16)(001), 4.65(10)(111), 3.50(20)(210), 2.983(100)(014), 2.685(13)(121), 2.678(11)(205), 2.625(19)(311), and 2.187(15)(402). The crystal structure was determined using single-crystal X-ray diffraction data and refined to R1( F ) = 1.73% for 2864 9observed9 reflections with F o > 4σ( F o ). Vastmanlandite-(Ce) is nearly isotypic to gatelite-(Ce), ideally Ce 3 CaAl 2 AlMg[Si 2 O 7 ][SiO 4 ] 3 O(OH) 2 , and can be described as a regular dollaseite-(Ce)-tornebohmite-(Ce) polysome. The occurrence of extremely weak, continuous streaking in the diffraction patterns, and the presence of two pairs of mirror-related atoms in the tornebohmite-(Ce) module indicate that the structure model represents an average structure, unlike the situation in gatelite-(Ce) where there are no continuous streaks but instead, due to atomic ordering, sharp superstructure reflections resulting in a different unit cell.

Multi-analytical approach to solve the puzzle of an allanite-subgroup mineral from Kesebol, Västra Götaland, Sweden

Abstract Dark-brownish, euhedral crystals of an “allanite-like” mineral occur in a hematite-impregnated Mn-silicate rock at Kesebol, Västra Götaland, Sweden, associated with gasparite-(Ce), chernovite- (Y), rhodonite, andradite, manganoan calcite, and quartz. A structural study was carried out on single crystals-untreated, heated in air, and heated under inert atmosphere-combined with Mössbauer spectroscopy and TEM investigation. In all the untreated crystals the mean distance indicates that Me²⁺(Me = Mn, Fe) prevails at this site ( in the range 2.169-2.180 Å), in contrast with chemical data obtained by EPMA that yield a simplified formula Ca(REE³⁺ ⅔ ⃞ ⅓)Me3 ³⁺(SiO4)(Si2O7) O(OH), when normalized to Si = 3.00 apfu. Moreover, when a crystal is heated in air, all geometrical and structural variations indicate the development of an oxidation-dehydrogenation reaction, thus confirming that M3 is occupied by divalent cations before heating. The corresponding dehydrogenation is confirmed by a dramatic lengthening of the donor-acceptor distance. A crystal was annealed under inert atmosphere to verify possible effects of radiation damage on the polyhedral volumes. After prolonged annealing at 700 °C, a slight decrease of the unit-cell parameters is observed, suggesting restoring of crystallinity from a “partially metamict” state. Nonetheless, even in the annealed crystal, the distance is still consistent with a dominance of divalent cations at the M3 site. For all the examined crystals, structural data point to an octahedral cation population as follows: M1 = (Me³⁺, Al); M2 = (Al, Me³⁺); M3 = (Me²⁺, Me³⁺). This assumption is also in agreement with the Mössbauer spectrum, which was fitted to two Lorentzian quadrupole doublets for Fe³⁺ and one for Fe²⁺. Values of the isomer shifts (0.36 and 0.37 mm/s for Fe³⁺; 1.11 mm/s for Fe²⁺) and the quadrupole splitting (1.96 and 1.02 for Fe³⁺; 1.90 for Fe²⁺) show that Fe²⁺ (~12% of the total iron) is located in M3, while Fe³⁺ occupies M1 and, to lesser extent, M2. TEM-EDS investigations have revealed chemical heterogeneities related to different degree of radiation damage. In particular, areas showing poor crystallinity are relatively enriched in Si and O with respect to the highly crystalline areas, thus suggesting that EPMA chemical data are biased by the presence of metamict areas enriched in SiO2 and likely in H2O. EPMA data were therefore corrected for the excess of silica. The cation population after correction is in keeping with the structural and spectroscopic data. Disregarding minor substitutions, the ideal chemical formula for the epidote-group mineral from Kesebol is CaREEFe³⁺AlMn²⁺(Si2O7)(SiO4)O(OH), which is related to ferriallanite-(Ce) by the substitutional vector M3(Mn²⁺) → M3(Fe²⁺).

PARAGENESES AND COMPOSITIONAL VARIATIONS OF SB OXYMINERALS FROM LANGBAN-TYPE DEPOSITS IN VARMLAND, SWEDEN

Abstract The Långban, Nordmark and Jakobsberg Mn-Fe deposits contain the only known occurrences of filipstadite and manganostibite (ideal formulae (Mn, Mg)2(Sb0.5+5 Fe0.5+3 )O4 and Mn72+SbAsO12, respectively). Filipstadite from Nordmark is newly recognized, and occurs in assemblages with svabite-johnbaumite, calcite, tephroite-forsterite, phlogopite-kinoshitalite, tilasite, ±jacobsite, ±plumbian roméite, ±adelite, ±hedyphane. Manganostibite from Långban and Jakobsberg is reported for the first time, and the mineral is generally associated with katoptrite, tephroite, humite-group minerals, calcite, svabite, allactite, manganosite, hausmannite, jacobsite, spinel s.s., etc. Whereas filipstadite is clearly secondary relative to the major part of the matrix components, manganostibite is believed to have formed coevally with the principal ore and skam minerals at these deposits. The previously known compositional ranges are extended. Based on electron-microprobe analyses, Nordmark filipstadite contains 4.1−7.3 MgO, 0.0−0.5 Al2O3,30.5−45.3 MnO, 17.0−40.1 Fe2O3, 0.2-0.9 ZnO, 19.9−29.9 Sb2O5 (all in wt.%), corresponding to 58−100 mol.% of a pure filipstadite component. Associated jacobsites show Sb2O2 contents of up to c. 5 wt.%. Manganostibites (all three deposits considered) contain 1.0−2.9 MgO, 2.8−3.8 Sit2, 57.4−60.3 MnO, 0.2-3.5 Mn203, 0.3-2.0 Fe203, 0.0-2.4 ZnO, 21.5−23.0 Sb2O5, 7.7−10.0 As2O5 (all in wt.%). Si and trivalent cations are incorporated via a (Mn3+ ,Fe3+) + Si4+ = Mn2+ + As5+ exchange mechanism, which improves the local charge-balance at tetrahedral structural sites dominated by As.

Crystal chemistry of REEXO4 compounds (X = P, As, V). I. Paragenesis and crystal structure of phosphatian gasparite-(Ce) from the Kesebol Mn-Fe-Cu deposit, Västra Götaland, Sweden

A new occurrence of the rare arsenate species gasparite-(Ce), ideally CeAsO 4 , is reported from the Kesebol Mn-Fe-Cu deposit in south-western Sweden, where it occurs as yellowish euhedral crystals up to 0.5 mm in maximum size, in association with rhodonite, andradite, Mn 2+ -dominant “allanite-(Ce)”, chernovite-(Y), manganoan calcite and quartz. All gasparite samples studied are phosphatian, and quantitative SEM-EDS analyses of two representative grains gave the following average compositions: Ce 0.77 La 0.10 Nd 0.10 Pr 0.02 Ca 0.01 Th 0.007 [As 0.84 P 0.12 Si 0.03 ]O 4 and Ce 0.79 La 0.11 Nd 0.11 Th 0.010 [As 0.85 P 0.11 Si 0.02 ]O 4 . The Kesebol gasparite-(Ce) is distinguished from the type material by a higher Ce/REE tot ratio and a significant P content. The crystal structure of phosphatian gasparite-(Ce) has been determined from single-crystal X-ray diffractometer data (Mo Ka radiation, CCD area detector) and refined in space group P2 1/n to R(F) = 2.86 % for 776 ‘observed’ reflections with F o > 4σ( F o ) ( a = 6.929(3), b = 7.129(3), c = 6.697(3) A, β = 104.46(3)°, V = 320.3(2) A 3 , Z = 4). The results confirm that gasparite-(Ce) has a monazite-type structure, and give the idealised formula (Ce, La, Nd)[(As 0.71 P 0.29 )O 4 ].

Percleveite-(Ce) — a new lanthanide disilicate mineral from Bastnäs, Skinnskatteberg, Sweden

Percleveite-(Ce), (Ce, La, Nd) 2 Si 2 O 7 , is a new mineral species from the Bastnas Fe-Cu-REE deposit, Skinnskatteberg, Vastmanland, Sweden. It occurs closely associated with mainly cerite-(Ce), bastnasite-(Ce) and quartz. The colour is greyish and the luster greasy to resinous. The anhedral crystals, up to 0.5 mm in size, are colourless in thin section and optically uniaxial (+). H ∼ 6. Cleavage is imperfect parallel to {001}. Electron-microprobe analyses give: La 2 O 3 14.66, Ce 2 O 3 31.36, Pr 2 O 3 3.41, Nd 2 O 3 12.97, Sm 2 O 3 2.69, Gd 2 O 3 2.26, Dy 2 O 3 0.53, Ho 2 O 3 0.07, Er 2 O 3 0.21, Yb 2 O 3 0.04, Y 2 O 3 2.93, CaO 0.10, FeO 0.01, SiO 2 26.55, sum 97.79, yielding the empirical formula (Ce 0.87 La 0.41 Nd 0.35 Y 0.12 Pr 0.09 Sm 0.07 Gd 0.06 Dy 0.01 Ca 0.01 ) Σ=1.99 Si 2.01 O 7 based on 7 O atoms. The mineral is shown to be isostructural with the synthetic, low-temperature lanthanide disilicates (general formula Ln 2 Si 2 O 7 ) with tetragonal symmetry (space group P 4 1 ). Unit-cell parameters are a = 6.7805(8) and c = 24.689(4) A (refined from powder data) with Z = 8. The structure has been refined from single crystal data to a weighted Rw value of 0.036. All four symmetry independent Ln positions are slightly differently occupied by the lanthanide ions. Percleveite is formed at conditions with slightly higher SiO 2 activities, and lower concentrations of Ca and Mg, than conditions favourable for the crystallization of cerite-(Ce).

Chiavennite and zoned genthelvite-helvite as late-stage minerals of the Proterozoic LCT pegmatites at Utö, Stockholm, Sweden

Abstract The Utö pegmatite system is host to a plethora of late-formed minerals, most of which have not been detected in previous studies of this classical locality. Among them are minerals that developed in cracks and druses, including a number of beryllosilicates, like the zeolite chiavennite, genthelvite-helvite, milarite and bavenite; Mn-rich minerals such as manganite, wickmanite and friedelite; and several sulphides. The parageneses and crystal chemistry of chiavennite and genthelvite-helvite are the focus of the present paper. Chiavennite was analysed using electron and ion-microprobe techniques, and was found to contain significant amounts of B substituting for Be: a structural formula for one sample is (Ca0.93Na0.07)Mn0.77Fe2+ 0.10Ca0.07Fe3+ 0.06Mg0.01) [Be1.86B0.15][Si4.68Al0.32]O12.86(OH)2.14 · 2H2O. The corresponding orthorhombic unit-cell parameters are a = 8.907(4), b = 31.227(9), and c = 4.777(2) Å. The genthelvite-helvite grains, often arranged in polycrystalline aggregates, are zoned discontinuously reflecting variations in Mn and Zn contents. Generally, they have Mn-rich cores and Zn-dominant rims (consisting of up to 93 mol.% of the genthelvite end-member). The late-stage Be minerals are products of low-temperature alteration of primary beryl under the influence of Ca- and Mn-rich fluids.

Lanthanide mineralizations of Bastnäs type: overview and new data

Skinnskatteberg district, Sweden, where mining activities aiming for primarily iron and copper occurred already 500 years ago. The scientific study of Bastnäs started at the time when Cronstedt (1751) described an unknown reddish substance called “Bastnäs Tungsten”, presently known as cerite-(Ce). This mineral was the source from which a new element was isolated by Hisinger & Berzelius (1804), named cerium after the asteroid Ceres observed shortly before. Further discoveries of new chemical elements (e.g. La) and minerals (e.g. bastnäsite) gave this remarkable locality a definite place in the history of science. Despite this, no attention has been paid to it from an ore-genetical point of view since Geijer’s (1961) work, where he introduced the term “Bastnäs type” by including some other deposits, in the Norberg district, with a putatively common origin. The present study also includes the Rödbergsgruvan deposit, Nora district, where lanthanide mineralization was recognized more recently. The deposits are restricted to a narrow, NE–SW trending zone of c. 80 km length, situated in the Bergslagen region where the oldest bedrock is dominated by supracrustal Svecofennian rock sequences, comprising mainly felsic metavolcanites and marbles. The metavolcanic rocks have been hydrothermally altered at an early, volcanic stage and later became metamorphosed under amphibolite-facies conditions. The supracrustal units are intruded by two generations of granitoids. The older (1.90–1.85 Ga) intrusions range from tonalite to granite in composition and are normally foliated, whereas the younger (1.80–1.77) Ga are essentially undeformed normal granites. The bedrock underwent ductile deformation in connection with the Svecofennian orogeny at c. 1.85 Ga, while later movements have caused fracturing and faulting affecting all types of rock in the area. At Bastnäs the lanthanide-bearing skarn-magnetite-sulfide assemblages have completely replaced a carbonate body that occurred adjacent to a quartz-banded Fe-ore. In the deposits of the Norberg district, the mineralization occurs as disseminations and skarn replacements in dolomite marble. Petrographic studies and electron-microprobe analyses have been carried out to document paragenetic and mineral-chemical relations. Based on their REE mineral assemblages, it has been proposed (Holtstam & Andersson 2002) to divide the deposits into two subtypes: one almost exclusively with LREE-enrichment (type 1) and another showing enrichment of both LREE and Y (type 2). The presence of Fand Be-silicates is also characteristic for the second type. Type 1 (Rödbergsgruvan and Riddarhyttan) is dominated by assemblages of cerite-(Ce), allanite-(Ce), bastnäsite ± törnebohmite-(Ce) ± fluocerite. The dominant gangue mineral is tremolite-actinolite. Our paragenetic observations are in general agreement with older descriptions of the Bastnäs deposit (e.g. Geijer 1921). Bastnäsite occurs both as a primary phase, which seems to have crystallized mainly after cerite and allanite, as well as a fine-grained alteration product of cerite-(Ce). The Ce/La ratios of the bastnäsite Lanthanide mineralizations of Bastnäs type: overview and new data

Tegengrenite, a new, rhombohedral spinel-related Sb mineral from the Jakobsberg Fe-Mn deposit, Värmland, Sweden

Abstract Tegengrenite, forming octahedra up to 150 μm in size, occurs associated with hausmannite, calcite, brucite, dolomite, clinohumite, kinoshitalite, native copper, barytocalcite, bindheimite, and cerussite in Mn ore from Jakobsberg, Filipstad district, Värmland, Sweden. The mineral is deep red and translucent, with a sub-adamantine luster. In reflected light it is gray and nearly isotropic, with measured reflectance values (R%) 10.4 (λ = 470 nm), 10.0 (546 nm), 9.9 (589 nm), and 9.8 (650 nm). The refractive index at λ = 589 nm is 1.92(2). There is no cleavage; fracture is conchoidal. Dcalc is 4.58(1) g/cm3. Electron-microprobe analyses gave (average of 35 points; in wt%) MgO 21.83, Al2O3 0.76, SiO2 1.70, Sb2O5 36.13, TiO2 1.40, Fe2O3 0.78, MnO 25.74, Mn2O3 (calculated from stoichiometry) 8.14, ZnO 2.66, sum 99.14, yielding the empirical formula Mg2+1.22Mn2+ 0.82Zn0.07 (Sb0.50Mn3+ 0.23Si0.06Ti0.04Al0.03Fe0.02)O4. Combined X-ray and electron diffraction studies show that tegengrenite is rhombohedral, space group R3̄ or R3, and pseudocubic. The individual tegengrenite octahedra consist of eight twin domains that give rise to complex diffraction patterns and make them unsuitable for a conventional structure determination. Tegengrenite, like the chemically related mineral filipstadite, bears a close structural relationship to spinel. The eight strongest lines in the X-ray diffraction pattern are [d (in angstroms) (I/I0)(hkl)]: 4.98(20)(211, 003), 4.32(19)(122), 4.24(18)(113), 3.052(33)(140, 214), 2.608(100)(241, 143, 125), 2.162(28)(244), 1.665(30)(363, 075), 1.531(26)(820) and 1.527(29)(428). The refined unit-cell parameters (hexagonal setting) are a = 16.196(1) and c = 14.948(2) Å with Z = 42; for the cubic spinel-type subcell A = c/√3 - = 8.63 Å. The new species is named for Felix Tegengren (1884-1980).

Jinshajiangite from the Norra Kärr alkaline intrusion, Jönköping, Sweden

Abstract The second world occurrence for jinshajiangite has been encountered at Norra Karr, where the mineral appears as tabular grains up to 4 mm long, essentially in albite veinlets. Associated phases are, inter alia, magnesio-arfvedsonite, aegirine, fluorapatite and rosenbuschite. Refinement of the monoclinic unit-cell parameters gave a = 10.696(2) A, b = 13.800(5) A, c = 20.705(3) A, β = 94.96(2)° and V = 3044.7(5) A3. The Norra Karr jinshajiangite is chemically distinguished from the type material mainly by a higher Fe2+/(Fe2+ + Mn) ratio. It is interpreted as a late-magmatic product related to fractionation.