Gunnar Raade

Replacement textures involving four scandium silicate minerals in the Heftetjern granitic pegmatite, Norway

Four late-hydrothermal scandium silicate minerals, related by replacement textures, were studied by EMPA and SIMS. Textural evidence shows that early-formed thortveitite is broken up by bazzite and scandian milarite, which seem to occur in equilibrium. Thortveitite is also partly replaced by kristiansenite. The two steps of alteration involve first the introduction of fluids rich in Be, K, Ca and Cs to form bazzite and milarite and then Ca and Sn for the formation of kristiansenite. Addition of water accompanies both steps. Thortveitite is unusually rich in SnO 2 (up to 5.67 wt.%). The amount of Sn is balanced by Mn according to the substitution scheme 2Sc 3+ ⇔ Sn 4+ + Mn 2+ . Bazzite is strongly zoned with respect to Cs and has up to 8.55 wt% Cs 2 O. The alkali content in the structural channels is balanced by Fe 2+ and Mn 2+ substituting for Sc. Scandian milarite is close to the end-member formula K(CaSc)Be 3 (Si 12 O 30 ) with nearly all Al replaced by Be and half of the Ca atoms by Sc. Kristiansenite is very near to the ideal formula Ca 2 ScSn(Si 2 O 7 )(Si 2 O 6 OH).

Heftetjernite, a new scandium mineral from the Heftetjern pegmatite, Tørdal, Norway

Heftetjernite, ideally ScTaO 4 , is a new scandium mineral from the Heftetjern pegmatite, Tordal, Telemark, Norway. In the type specimen, it occurs as minute, elongate tabular, very dark brown crystals in a single small void in albite. Other associated minerals are fluorite, muscovite, altered milarite, a metamict, dark greyish brown mineral of the pyrochlore-microlite group, and an unidentified, orange-brown, tabular, nearly X-ray amorphous Ti-Y-Ta-Nb-mineral. Electron-microprobe analysis yielded the empirical formula (Sc 0.64 Sn 0.13 Mn 0.12 Fe 0.08 Ti 0.06 ) ∑1.03 (Ta 0.69 Nb 0.30 ) ∑0.99 O 4 which clearly demonstrates the charge-balanced substitution scheme 2Sc 3+ = (Sn,Ti) 4+ + (Mn,Fe) 2+ . The mineral crystallises in the wolframite structure type, with space group P 2/ c and a = 4.784(1), b = 5.693(1), c = 5.120(1) A, β = 91.15(3)°, V = 139.42(5) A 3 ( Z = 2). A synthetic equivalent is known. Strongest lines in the calculated X-ray powder diffraction pattern of heftetjernite are [ d in A( I ) ( hkl )]: 3.000 (100) (11–1), 2.9570 (97) (111), 3.662 (53) (110), 2.4877 (34) (02–1), 4.783 (33) (100), 3.807 (32) (01–1). The crystal structure was refined to R ( F ) = 1.39 % from single-crystal X-ray diffraction data (293 K). It is based on two types of edge-sharing, distorted octahedra occupied predominantly by Sc and Ta, respectively. Heftetjernite is translucent to transparent, with a dark brownish (with a reddish hue) streak and adamantine lustre. It is brittle, has a perfect {010} cleavage, irregular fracture and a Mohs hardness estimated to be around 4.5 by comparison to ferberite; D x = 6.44 g/cm 3 (from crystal-structure analysis). Optically, the mineral is biaxial with an unknown optical sign, weakly pleochroic (yellowish brown with a reddish tint to reddish brown), with no observable dispersion. A mean refractive index of 2.23 was calculated from the Gladstone-Dale relationship using the X-ray density. Heftetjernite is named after its type locality. The mineral is compared with synthetic ScTaO 4 , ScNbO 4 , iwashiroite-(Y) and formanite-(Y) (both nominally YTaO 4 ), and some comments are made on the relation to Sc-bearing ixiolite.

Gjerdingenite-Mn from Norway — a new mineral species in the labuntsovite group: descriptive data and crystal structure

Gjerdingenite-Mn occurs as orange-yellow to brownish prisms up to 1 mm long in miarolitic cavities of a sodic granite (’ekerite’) at Gjerdingselva, Lunner, Oppland, Oslo Region, Norway. The simplified formula is (K,Na) 2 (Mn,Fe) [(Nb,Ti) 4 (Si 4 O 12 ) 2 (O,OH) 4 ].6H 2 O. It is the Mn-dominant analogue of gjerdingenite-Fe, the Ti analogue of kuzmenkoite-Mn and a dimorph of organovaite-Mn. The mineral is monoclinic, C 2/ m , with a = 14.563(3), b = 13.961(3), c = 7.851(2) A, β = 117.62(3)°, V = 1414.3(6) A 3 , Z = 2. The crystal structure was refined to R ( F ) = 0.079 on the basis of 1207 observed reflections and is compared to the structure of gjerdingenite-Fe. The strongest five reflections of the X-ray powder-diffraction pattern [d obs in A ( I ) ( hkl )] are: 6.96 (100) (020, 001), 4.94 (80) (021), 3.22 (90) (42-1, 400, 40-2), 3.10 (80) (041, 022) and 2.510 (40) (44-1, 401, 40-3, 042). The mineral is optically biaxial (+) with α = 1.670(2), β = 1.685(2), γ = 1.775(5); 2V meas = 52(8)°, 2V calc = 46(5)°. The axial dispersion is weak, r a , Y = b . Mohs hardness is about 5; D calc = 2.93 g/cm 3 . The pseudo-orthorhombic crystals are twinned on {001}, elongate along [010] and show the forms {001}, {100}, {201} and {021}. Some general aspects on the formation of labuntsovite-group minerals are discussed.

Powder X-ray diffraction data for goosecreekite [CaAl[sub 2]Si[sub 6]O[sub 16]⋅5H[sub 2]O]

X-ray powder data originally published for the zeolite mineral goosecreekite are of poor quality. The new data reported here for material from Norway are compared with powder data calculated from the published structure. The cell is monoclinic (space group P 2 1 , Z =2), a =7.422(2) A, b =17.414(4) A, c =7.288(2) A, β=105.43(3)°, V =907.9(3) A 3 . F 30 =32.75(0.023,40).

Si-rich bergslagite from a granitic pegmatite at Tennvatn, north Norway

Abstract Si-rich bergslagite from an amazonite-cleavelandite pegmatite at Tennvatn in Sørfold, Nordland, north Norway, has the empirical composition Ca1Ca1.00 Ca2Ca0.068(Be0.94Si0.06)(As0.774Si0.226)O4[(OH)0.97 O0.03], based on a single-crystal structure refinement (MoKα radiation, CCD area detector, 293 K, space group P21/c, a = 4.878(1), b = 7.810(2), c = 10.130(2) Å, β = 90.09(3)[ddot], V = 385.92(15) Å3, Z = 4, R1(F) = 4.48%) and electron-microprobe analyses of Ca, As and Si. The structure refinement revealed the presence of a previously unknown, partially occupied and octahedrally coordinated Ca2 site that provides charge-balance compensation. The sample has the highest content of Si ever reported in bergslagite, and can be compared to (As0.87Si0.08) found in bergslagite from the type locality (Långban, Sweden). The results also indicate that the previously postulated OH substitution scheme in type bergslagite is erroneous. Substantial substitution of Si for As in arsenates and arsenosilicates seems to be relatively rare; some examples are discussed.

Alflarsenite, a new beryllium-silicate zeolite from a syenitic pegmatite in the Larvik plutonic complex, Oslo Region, Norway

Alflarsenite is a new beryllium-silicate zeolite with chemical composition close to NaCa 2 Be 3 Si 4 O 13 (OH)·2H 2 O. It is a late-stage hydrothermal mineral from a syenitic pegmatite in the Tuften larvikite quarry, Tvedalen, Larvik, Vestfold, south Norway. Closely associated minerals are calcite, analcime and K-feldspar. Alflarsenite is monoclinic, P 2 1 , with a = 7.1222(4), b = 19.8378(11), c = 9.8071(5) A, β = 111.287(1)°, V = 1291.1(2) A 3 , Z = 4. The crystal structure was refined from single-crystal X-ray data to R 1 = 0.045 for 3283 observed reflections. The zeolite structure is novel, consisting of intersecting channels: 5- and 8-membered channel rings along [010] and 3-, 6- and 8-membered channel rings along [100]. The strongest eight reflections of the X-ray powder-diffraction pattern [ d (obs.) in A ( I ) ( hkl )] are: 9.095 (100) (001), 6.279 (42) (−111, 110), 4.189 (32) (−122, 121), 3.972 (76) (−141, 140), 3.205 (37) (−113, 112), 2.964 (70) (−232, 230), 2.915 (92) (−133, 132), 2.757 (33) (−242, 240). Alflarsenite crystals are colourless (in aggregates pale beige) and bladed; they are flattened on (010) and elongate on [100]. Identified crystal forms are {010}, {0–10}, {001} and {20–1}. Cleavage was not observed. The mineral is biaxial (+) with refractive indices α 1.578(1), β 1.580(1), γ 1.583(1), measured at 590 nm. 2 V (meas.) = 82(5)° from extinction curves and = 76(5)° by the Kamb method; 2 V (calc.) = 79°. The optical orientation is Z = b , X ^ a = 45(2)°. The Mohs hardness is ~ 4; D (calc.) = 2.605 g/cm 3 .