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An Unusual Titanium-Rich Oxide Mineral from Oslo, Norway Tovr Vrcron

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An Unusual Titanium-Rich Oxide Mineral from Oslo, Norway Tovr Vrcron American Mineralogist, Volume 69, pages 36E-390,I9U An unusual titanium-rich oxide mineral from Oslo, Norway Tovr Vrcron Secersrno Mineralo gic al-Ge olo gic al M us e um, Universityof Oslo Sars gate l, Oslo 5, Norway Abstract An unusual Ti-rich oxide mineral of composition Sre.21REEs.26Sis.a3Ti1a.0oFe3.5sV1.2s Cr1.5sO3shas been found in an anatase-albititedike at Oslo, Norway. The mineral is metamict becauseof a small Th content, and contains abundant water (12.14 wt.Vo\.It is black with a metallic to adamantine luster and gives a black-brown streak. The Mohs hardnessis 6. The reflectivity is 17.0-17.4%(546 nm) in air, weakly anisotropic. Heating in air or nitrogen gives X-ray powder lines of rutile (7fi), 8fi), and 900"C)or brannerite (10fi) and 12fi)'C). The chemistry of the mineral resemblesthat of crichtonite. 0ccurrence endothermicpeak. This is believed to representmetamict Three samples containing small, black, shiny crystals water loss. The microprobe analysis, including 12.14 surrounded by reaction halos and occurring in a 20-cm wt.Vowater,totals 10il..78%,assuming all iron to be Fe3*. wide dike were sampled by the author during 1965in a Traces of Y, Pr, Eu, Tb, and Ho were also found. All other elements were below their limits of detection as quarry for road-material (Huken Quarry) near the aban- doned Aanerud copper mine near Grorud in Oslo. The seen by spectrometer scanning. material has subsequently been removed by quarrying Table I shows the unit cell contents normalized to 6 operations and spread over the streets of Oslo. The and 38 oxygens, assuming all water as metamict water (see (Fe3*,Cf*, mineral occurs as pseudocubes up to 2 mm in size. above). The formula can be written as Microscopic investigation of polished sections revealed V5+)Ti2O6 or as S16.21REEs.265i0.43Til4.qoFcr.soVr.za some scattered inclusions of galena, and the mineral is Cr1.56O3s,assuming iron and vanadium in their highest often rimmed by pyrrhotite. Thin sectionsand powder X- oxidation states. ray photographs of the extremely fine-grained dike matrix X-ray crystallography showed the presenceof quartz, albite and anatase,mak- ing it an anatasealbitite dike. Unheated mineral material gave no X-ray diffraction pattern, due to its metamict state. To achieve X-ray data Chemical analysis the mineral was first recrystallized in two ways: in air at Electron probe microanalyses of polished sections 1000"Cfor 12 hours, and in nitrogen at 10fi)'C for 2 hours (Table were made on an ARL-Eux microprobe at the Central 2). The X-ray data were identical for these two pattern Institute of Industrial Research, Oslo, using a series of runs, showing the X-ray of brannerite. Heating in gave natural and synthetic standards (Amli and Grifrn, 1975; nitrogen at 12fi)'C for 2 hours also brannerite X-ray patterns. Segalstad and Larsen, 1978). Matrix corrections were Heating in air at temperatures lower than produced made according to Bence and Albee (1968),using correc- 1000'C , for duratiuons up to 8 days, rutile X- patterns (Table tion factors from Albee and Ray (1970),Amti ana Griffin ray 2). (1975), and Albee (pers. comm., 1977). The rare-earth properties elements (\EE) were analyzed,by the procedure de- Physical scribed by Amli and Grifrn (1975), using the same stan- The mineral occurs as 1-2 mm black pseudocubes, dards with the same accuracy as in their work. The showingu.stnllic to adamantineluster. Cross-like devel- analytical results, which represent the mean of four opment is also found. It gives a black-brown streak with a analyzed points, are presented in Table 1. No composi- reddish tint and is brittle with a conchoidal fracture. The tional zoning was observed. Mohs hardnessis 6. The Vickers microhardnesswas not The mineral was heated from 20'C to 12fi).C in a measured due to the small amount of material and the nitrogen gas atmospherein a "derivatograph" (combined brittle nature of the mineral. It is weakly anisotropic in DTA + DTGA + TGA instrument) at the Department of reflected light. The reflectivity is 17.0-17.4%at 546 nm in Chemistry, University of Oslo. A weight loss of 12.14% air, measured with a Zeiss reflectometer calibrated was experienced up to 80"C, associated with a broad against Zeiss standards and corrected for secondary 0003-004)uE4l0304-0388$02.00 3EE SEGALSTAD: TITANIUM.RICH OXIDE FROM NORWAY Table l. Chemical composition (wt.% oxides) and unit cell Table 2. Heating experiments of the Ti-rich oxide mineral from contents(number ofatoms assuming6 and 38 oxygens)ofthe Ti- Oslo, NorwaY. rich oxide mineral from Oslo. Norwav. tenDerature duration atmogphere pattern 'l N, branner.i te 0=6 0=38 zoo"c 2 h 't2 h air bronnexite Ti0, 55.93 2.0398 12.9187 r ooooc si0, 1.28 .0619 .3920 looooc 2h N2 branner-ite .45 .1 628 Al r03 .0257 goooc 24h air rutile Fe203 13.99 .5107 3 .2344 Mn0 .08 .0031 .0t96 goooc 67h air rutile .1? .0089 .0564 ttg0 zoooc Bd arD rutile ca0 .0129 .0817 Sr0 1,tl .0313 .198? Cr203 6.01 .2305 r.4598 Vu0s 5.84 .1872 1.1855 Scz0r ,0231 .1463 Zr02 .0025 .0158 analyzed. The X-ray pattern of his "anisotropic phase" l{a20 .t3 .01?9 ,0817 Kz0 .22 .0134 .0849 resembles somewhat that of the Oslo mineral heated to Th02 .38 .0042 .0265 Laz0r 1.22 .0218 .1381 1000'C.and the occurrence is similar, in that the albititic Ce203 A7 .0155 .0982 physical properties axecommon to Hz0 12.14 host rocks, habit and both. The chemistry of Mathiesen's mineral from Bidjo- |00,78 vaggeresembles that of davidite. The work by Patchett and Nuffield (1960) on the synthesisofbrannerite suggeststhat brannerite regainsits glare. The specific gravity, determined using pycnome- original structure on ignition. Although there is no differ- ters filled with toluene at 20"C. is 4.02 for the unheated ence between the X-ray data of brannerite and the Oslo mineral. mineral when heatedto 1000"Cin air and in nitrogen, and the derivatograph runs showed no peaks other than the Discussion one DTA peak assumedto be associatedwith the release The crichtonite group contains a number of related of metamict water, it is not believed that the Oslo mineral mineral speciesof the type AB21O3g,which are character- is isostructural with brannerite. The fairly large amount of ized by their predominant large cations, i.e., crichtonite transition metals is believed to make the rutile structure (Sr), senaite (Pb), davidite (REE + U), landauite (Na), also unsuitablefor this mineral. Rather, it is reasonableto loveringite (Ca), lindsleyite (Ba), and mathiasite (K) believe on the basis of the chemistry that this unusual (Gatehouseet al., 1978;Haggerty et al., l9E3). A rheni- titanium-rich oxide mineral belongs to the crichtonite um-rich titanium and iron oxide of the crichtonite series group (Hey et al., 1969; Grey et aI., 1976). The high was reported by Sarp et al. (1981). A large number of amount of metamict water probably makes it difrcult to Af,lo.6 minerals containing Ca, REE, U, Th, Nb, Ta, Ti, reconstitute the metamict mineral to its original structure. etc. belong to the euxenite, aeschynite, and brannerite Grey et al. (1976)found that in crichtonite and related groups. Moreover, Povilatis (1963)considered that bran- minerals Sr, Pb, and REE occupy only one of the nerite (ideally UTizOe) and thorutite (ideally ThTi2O6) available 39 anion sites in the unit cell. The formula can form a complete series of solid solutions. However, be expressedas A1-^B21O3,where B is largely Ti, Mn, Fleischer (1963) pointed out that the chemical analyses Fe, and the variable x indicatesthat full occupation of the presentedby Povilatis show a gap from Ths.21to Ths.s7. anion site by large cations is not always achieved,A being Due to the ionic radii of the elementsinvolved it may be REE, Pb, Sr, Ca, Th, K, Na, efc. Among the large difficult for other cations to substitute for U and Th in the cations, Sr is predominant in the Oslo mineral, as in the brannerite-thorutite structure to any large extent. crichtonite sample from Dauphin6, France (Grey et al., A vanadium-dominatedtitanium oxide, V2Ti3Oq,called 1976).The amount of Sr is, however, only one fourth of schreyerite by Medenbach and Schmetzer (1978), has that in the French crichtonite. The largest difference is in also been reported, and synthetic compounds similar to the large amount of chromium and vanadium replacing schreyerite have been described (Grey and Reid, 1972); iron in the Oslo mineral. The Oslo mineral would have the Grey et al., 1973). A polymorph of schreyerite, called structural formula ,4.6.71Br s.ssOre, while the French miner- kyzulkumite, was reported by Smyslova et al. (1981). al has Ao.e,BzrOre. Some unnamedtitanium-rich oxide minerals have been Haggerty et al. (1983) point out that the AF,B21O3g found, eontaining fairly large amounts of Cr, Y, Zr, Ca, minerals have TiO2 contents lying in a "window" be- Fe, etc. (Cameron, 1978, 1979; Mathiesen, 1970). Al- tween ilmenite at lower TiO2 contents, and rutile at higher though Cameron's mineral description is not accompa- values. The TiOz content of the Oslo mineral (56 wt.%) is nied by X-ray data, he believed his minerals to belong to more like the value for davidite (-55 wt.%\ than for the pseudobrookite or the crichtonite groups. Mathie- crichtonite (-60.5 wt.Vo). sen's mineral description is accompaniedby incomplete Total content of REE is higher than the content of Sr, a chemical analysesand some X-ray powder data, but it is fact also characteristic of davidite, however, the Oslo difrcult to determine from the data which mineral he mineral lacks U, which is a specific constituent of davi- SEGALSTAD: TITANIUM-RICH OXIDE FROM NORWAY dite.
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