Polylithionite from Syenite Pegmatite at V Øra, Sandefjord, Oslo Region, Norway
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Polylithionite from syenite pegmatite at V øra, Sandefjord, Oslo Region, Norway. Contributions to the mineralogy of Norway, No. 65 GUNNAR RAADE & ALF OLA V LARSEN Raade, G. & Larsen, A. 0.: Polylithionite from syenite pegmatite at Vøra, Sandefjord, Oslo Region, Norway. Contributions to the mineralogy of Norway, No. 65. Norsk Geologisk Tidsskrift, Vol. 60, pp. 117-124. Oslo 1980. ISSN 0029-196X. Polylithionite from Vøra has a chemical composition close to the ideal end-member formula KLi,AIS40,0F,. It has the l M polytype structure with a= 5.196(4), b= 8.960(4), c= 10.051(4) Å, f3 = 100.29(5)0• The measured density is 2.82(1) gjcm3, the calculated density 2.84 gjem•. Optical measurements gave f3 = 1.556(1) , 'Y= 1.559(1) , 2Va = 43(3)0 on one sample and ,B = 1.551(1), 'Y= 1.555(1) on another. DTA/TGA curves and infrared spectrum are given. The mineral paragenesis of the V øra syenite pegmatite is reported, and data are given that indicate enrichment of Li in the dark mineral constituents. The Gladstone-Dale relationship applied to micas is shown to give better agreement between calculated and measured mean refractive index using k-values from Larsen & Berman (1934) than using the values of Mandarin o (1976) . G. Raade & A. O. Larsen, Institutt for geologi, Universitetet i Oslo, Postboks 1047 Blindern, Oslo 3, Norway. The name polylithionite was introduced by identified as polylithionite, with a composition Lorenzen ( 1884) for a lithium-rich mica from dose to KLi2AlSi4010F2• Such micas are rela syenite pegmatites at Kangerdluarssuk, Green tively uncommon, occurring in some syenite land. BrØgger (1890: 195) described a lithium pegmatites as a late-stage formation. Apart from mica occurring as a rarity in syenite pegmatite on the Norwegian occurrences it is known only the island Lille ArØy in the Langesundsfjorden from Greenland (BØggild 1953, Semenov 1969), area. He was aware of the possible identity with the Kola peninsula (Vlasov et al. 1966, Semenov polylithionite, but lack of material prevented 1972), Siberia (Semenov et al. 1974, Sveshni further investigations. A semiquantitative kova et al. 1976:34-35), and Mont St. Hilaire, spectrographicanal y sis of the mineral by Oftedal Quebec, Canada (Perrault 1966). ' (1940 ) showed a lithium content similar to that of Because of its rarity and since no complete polylithionite from the original locality. data have been recorded on material from a A small specimen containing light-coloured single locality, the Vøra polylithionite is de mica plates l cm across, associated with K scribed in some detail in this pa per, and an feldspar, albite and aegirine, was collected by G. account of the mineral paragenesis of the pegma Raade from a pegmatite on the east side of Lille tite is presented. Arøy. It gives an X-ray powder pattern of the IM lepidolite structure type, typical for polylithion ites (Levinson 1953, Munoz 1968). Very small Occurrence amounts of a similar mica, associated with analcime and aegirine, were X-ray identified The polylithionite locality is situated at Vøra, from the island Låven in Langesundsfjorden. Vesterøya, some 8 km SSE of Sandefjord, in the The occurrence of polylithionite as a rare con southern part of the Oslo Region. Two very stituent of the syenite pegmatites in the coarse-grained syenite pegmatites are exposed in Langesundsfjorden area can thus be regarded as larvikite cliffs. The lower pegmatite forms a fairly well established. steeply dipping, irregular dyke, less than l m In 1976 a light mica was found in some wide, which can be followed for a distance of quantity in a syenite pegmatite near Sandefjord. 30-40 m. The upper pegmatite is exposed for a Preliminary investigations indicated an appreci shorter distance and it may possibly have been able lithium content. and it was subsequently connected with the lower one. There is a distinct 118 G. Raade & A. O. Larsen NORSK GEOLOGISK TIDSSKRIFT 2 (1980) difference in mineralogy between the upper and TabZe l. X-ray powder diffraction data lower pegmatites. Poly1ithionite, quartz, arf for polylithionite from Vøra, Sandefj ord. vedsonite, catapleiite, and monazite have only a = 5.196(4) Å b 8.960(4) Å been found in the upper dyke, whereas astro c = 10.051(4) Å s 100.29(5)0 phyllite, biotite (rare), eudidymite, and thorite seem to be confined to the lower dyke. dcalc(Å) I/Il The main mineral is a greyish to brownish K-feldspar, occurring in individuals up to 20 cm. 001 9.93 9.89 45 Aegirine and barkevikite are widespread, the 002 4.95 4.94 100 020 4.482 4.480 25 latter especially in the northern part of the lower 110, ho 4.446 4.440 15 pegmatite. Aenigmatite is also common, in ir In 4.318 4.308 15 regular masses up to 20 cm across. Small 021 4.083 4.081 15 amounts of anatase were identified as a sec 111 3.829 3.835 15 ondary product after aenigmatite. Euhedral apa ll2 3.594 3.593 40 tite crystals are often met with, and may show 022 3.324 3.320 50 alteration to bastnasite. Fibrous masses of elpi 003 3.296 3.297 85 112 3.073 3.075 50 dite, frequently somewhat altered, are relatively l13 2.870 2.868 25 abundant, especially in the upper pegmatite. 023 2.656 2.655 20 Other minerals occasionally met with are albite, 2or 2.589 2.581 20 zircon, pyrochlore, and magnetite. In addition, 130, l30 } 2.579 epididymite, calcite, chlorite, and montmorillo 032 2.557 nite are sparingly present. 200, 2oo } 2.553 2.556 15 Aegirine, barkevikite, zircon, and apatite be l31 2.552 004 2.472 } 2.473 5 long to the early formed minerals in the pegma 113 2.470 tites, whereas aenigmatite, polylithionite, elpi 210, 210 } 2.458 2.460 5 dite, and quartz have crystallized later. Epididy 202 2.457 mite, albite, and calcite are among the youngest 131 2.443 2.442 5 formations. BrØgger (1890) also observed that 132 } 2.376 2.375 lO his lithium mica was younger than aegirine and 201 2.374 114 2.318 2.318 <5 K-feldspar. 221 2.242 } 2.241 5 The presence of larger amounts of aenigmatite 040 2.240 is a feature of considerable interest, since this 2o3 2.221 mineral has never been identified with certainty 220, 220 } 2.217 2.220 <5 in the syenite pegmatites of the larvikite area, 033 2.213 although BrØgger ( 1890: 432) claimed its probable 041 2.185 2.185 <5 existence in the Langesundsfjorden pegmatites. 222 2.154 2.154 <5 l33 2.126 Quartz and arfvedsonite are very rare con } 2.123 5 202 2.121 stituents of the pegmatites in Langesundsfjorden 005 1.978 1.978 30 (BrØgger 1890:12, 410), and elpidite is reported for the first time from Norwegian syenite pegma Philips diffractometer, graphite mono tites. chromator, CuKar (A= 1.54051 Å). Information on the mineralogy of the V øra Pb(N03)2 was used as internal standard. occurrence was given by R. Hansen and S.-A. Intensities were measured from peak (1968). Berge (pers. comm. 1976), who first observed heights. lndexing based on Munoz 20 these and other interesting pegmatites in the reflections were used for least squares refinement of cell parameters. vicinity of Sandefjord. agreement with that of synthetic l M polylithion ite with space group C2/m, as reported by X-ray crystallography Munoz (1968). Thus the Vøra polylithionite is X-ray powder diffraction data for polylithionite definitely the l M polytype, the other possible from V øra (grain-size < 0.063 mm) are given in polytypes (2M2 and 3T) being distinguishable Table l. Care was taken to avoid preferential from their X-ray powder data (Munoz 1968) or orientation. The powder pattern is in close optical properties. NORSK GEOLOGISK TIDSSKRIFT 2 (1980) Polylithionite from syenite pegmatite 119 The refined cell parameters for the V øra It is evident that these figures are significantly polylithionite are a= 5.196(4), b= 8.960(4), higher than those for the V øra polylithionite, but c= 10.051(4) Å, 13=100.29( W, V= 460.4(6) Å3• they are nevertheless consistent with earlier For comparison, the cell dimensions for polyli measurements on the Kangerdluarssuk material thionite from Kangerdluarssuk (Munoz 1968: by Larsen & Berman (1934: 161) reporting 1495) are a= 5.189, b= 8.974, c= 10.067 Å, a= 1.544, 13= 1.565, y= 1.566, 2Va= 40°, and 13= l 00°27', which gi ve V= 461.0 Å'1• from Hendricks & Jefferson (1939:758)'}' = 1.569 and 2Va= 40°. As is shown later, the chemical compositions Physical and optical properties of the V øra and Kangerdluarssuk polylithionites are almost identical (Table 2) and their cell The V øra polylithionite occurs as thick, irregular volumes and densities are very dose. It is there crystal books and aggregates with a very pale fore reasonable to expect that their refractive yellowish green colour, occasionally stained indices would be similar - in fact, the specific brownish by iron compounds. The individual refractive energies of the V øra and Kangerd mica plates may reach 5-6 cm across. The den luarssuk minerals are K = 0.2026 and K = 0.2028, sity was determined to 2.82(1) g/cm3 by the respectively, using the k-values of Mandarino sink/float method, using di-iodomethane diluted (1976) or K = 0.1998 and K = 0.2001 using the with acetone. The calculated density is 2.84 older k-values from Larsen & Berman (1934).