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Steele, Ian M.

Publications and source records attributed to Steele, Ian M..

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Shinkolobweite, from the Shinkolobwe Mine, Democratic Republic of Congo: A New Mineral Containing Uranium in the Rare Pentavalent Oxidation State

ABSTRACT Shinkolobweite, Pb1.333[U5+O(OH)(UO2)5O4.67(OH)5.33](H2O)5, is a new lead uranyl oxide-hydroxide hydrate mineral containing hexavalent and pentavalent uranium from the Shinkolobwe mine, Democratic Republic of Congo. Crystals of shinkolobweite are dark reddish-brown prisms up to 0.5 mm in length, occurring on a matrix of massive uraninite associated with fourmarierite, rutherfordine, soddyite, and sklodowskite. Crystals are translucent with subadamantine luster and light bronze-yellow streak, are flattened on {010}, are elongated on [001], and exhibit the forms {100}, {010}, {101}, and . The mineral is non-fluorescent under both longwave and shortwave ultraviolet illumination. It has a Mohs hardness of ∼2 and exhibits brittle tenacity with perfect cleavage on {010}, imperfect cleavage on {100}, and even fracture. The calculated density is 5.853 g/cm3 based on the empirical formula. Electron probe microanalysis provided the empirical formula Pb1.290U6+4.876U5+1.166O27H16.633 based on 27 O apfu and U5+:U6+ determined by X-ray photoelectron spectroscopy. Shinkolobweite is orthorhombic, superspace group Pnnm(0b0)000, a = 14.4808(4), b = 7.0681(8), c = 11.9423(3) Å, V = 1222.32(15) Å3, modulation wave vector [0 1/3 0], and Z = 2. The structure was refined from 8959 reflections to a final R1 = 0.0736 for all reflections. Uranyl oxide-hydroxide sheets in shinkolobweite adopt the β-U3O8 topology and possess (3 + 1) commensurately modulated ordering that results from the long-range ordering of U5+ and U6+ in the sheet, as well as the position and occupancy of interlayer Pb2+ cations. Observations of a topological transition between α-U3O8 and β-U3O8 type sheets in shinkolobweite supplements our understanding of U5+ mineral oxidation and stability.

Mineralogy↗
DOE OSTI2017

Leószilárdite, the first Na,Mg-containing uranyl carbonate from the Markey Mine, San Juan County, Utah, USA

Leószilárdite (IMA2015-128), Na 6 Mg(UO 2 ) 2 (CO 3 ) 6 ·6H 2 O, was found in the Markey Mine, Red Canyon, White Canyon District, San Juan County, Utah, USA, in areas with abundant andersonite, natrozippeite, gypsum, anhydrite, and probable hydromagnesite along with other secondary uranium minerals bayleyite, čejkaite and johannite. The new mineral occurs as aggregates of pale yellow bladed crystals flattened on {001} and elongated along [010], individually reaching up to 0.2 mm long. More commonly it occurs as pale yellow pearlescent masses to 2 mm consisting of very small plates. Leószilárdite fluoresces green under both longwave and shortwave ultraviolet light, and is translucent with a white streak, hardness of 2 (Mohs), and brittle tenacity with uneven fracture. The new mineral is readily soluble in room temperature H 2 O. Crystals have perfect cleavage along {001}, and exhibit the forms {110},{001},{100},{101} and {101}. Optically, leószilárdite is biaxial (-), α= 1.504(1), β= 1.597(1), γ = 1.628(1) (white light); 2V (meas.) = 57(1)°, 2V (calc.) = 57.1°; dispersion r > v , slight. Pleochroism: X = colourless, Y and Z = light yellow; X < Y ≈ Z . The average of six wavelength dispersive spectroscopic analyses provided Na 2 O 14.54, MgO 3.05, UO 3 47.95, CO 2 22.13, H 2 O 9.51, total 97.18 wt.%. The empirical formula is Na 5.60 Mg 0.90 U 2 O 28 C 6 H 12.60 , based on 28 O apfu. Leószilárdite is monoclinic, C2/m, a = 11.6093(21), b = 6.7843(13), c = 15.1058(28) Å, β = 91.378(3)°, V = 1189.4(4) Å 3 and Z = 2. The crystal structure ( R 1 = 0.0387 for 1394 reflections with I obs > 4σ I ), consists of uranyl tricarbonate anion clusters [(UO 2 )(CO 3 ) 3 ] 4- held together in part by irregular chains of NaO 5 (H 2 O) polyhedra sub parallel to [010]. Individual uranyl tricarbonate clusters are also linked together by three-octahedron units consisting of two Na-centred octahedra that share the opposite faces of a Mg-centred octahedron at the centre (Na–Mg–Na), and have the composition Na 2 MgO 12 (H 2 O) 4 . The name of the new mineral honours the Hungarian-American physicist, inventor and biologist Dr. Leó Szilárd (1898–1964).

Mineralogy↗
NASA NTRS1995

Mineralogy of a refractory inclusion in the Allende (C3V) meteorite

A spherical 220-micrometer diameter, spinel-hibonite-perovskite inclusion from the Allende C3V meteorite contains a central hibonite cluster with an angular coundary. This central hibonite is enclosed within spinel that is zoned from Mg-rich at the hibonite boundary to more Fe-rich at the inclusion boundary. This spinel zone includes lath-shaped hibonites usually subradial to the central hibonites. Two textural types of perovskites are present as exsolution from the central hibonite and as equidimensional grains within both the central hibonite and spinel. These second perovskites have exsolution lamellae of Al2O3. Within the central hibonite and adjacent to some equidimensional perovskites, a fine porous phase interpreted as alteration has a composition of nearly pure Al2O3 with minor amounts of Na and Si. This is possibly either an intergrowth of corundum and nepheline or a modified Al2O3, Beta-alumina.

Steele, Ian M.↗
NASA NTRS1993

Fe/Mn in olivine of carbonaceous meteorites

Olivines in primitive meteorites show a range of Fe/Mn both within one grain and among grains suggesting that they have recorded changing conditions during or after growth. Because olivine should be an early forming phase, Fe/Mn is used here to infer these earliest conditions. Initial Fe/Mn in cores of isolated, euhedral forsterite in both C2 and C3 meteorites ranges from 25 to 35 but differs at grain edge. Murchison (C2) forsterites show Fe/Mn approaching 1.0 at the grain edge while Ornans Fe/Mn is near 60 at grain edge. These values are lower than the matrix Fe/Mn for both meteorites and the distinct difference in zoning profile indicates different processes operating during and after grain growth. The Fe/Mn of bulk samples from a particular source such as the Moon is nearly constant. Individual samples show variation suggesting that there is some fractionation of Mn from Fe. Minerals have their individual ranges of Fe/Mn which has been used to recognize different types of olivine within one meteorite. Extreme values of Fe/Mn below 1.0 occur in forsterite from some IDP's, UOC matrix, and C1 meteorites. There are apparently no detailed studies of Fe/Mn variation within single olivine grains. Forsterite grains in C2 and C3 carbonaceous chondrites show complex zoning, and the nearly pure forsterites (Fo greater than approximately 99.5) have high levels of some minor elements including Ti, Al, V, and Sc. There is disagreement on the original source of these grains and both chondrule and vapor growth have been proposed. In addition, there is clear evidence that diffusion has affected the outer margins but in some cases the whole grain. Within the cores, the FeO range is limited, and if growing under constant conditions, the Fe/Mn should be near constant as there is little fractionation of Mn from Fe by forsterite. Additionally, there are apparently no co-crystallizing phases as evidenced by a lack of common inclusions in the forsterites. These observations are now followed by analyses of isolated olivine grains in C2 and C3 meteorites.

Steele, Ian M.↗
NASA NTRS1993

Chemical zoning and diffusion of Ca, Al, Mn, and Cr in olivine of springwater pallasite

The pallasites, consisting mainly of Fe-Ni metal and olivine, are thought to represent the interior of a planetary body which slowly cooled from high temperature. Although the olivines are nearly homogeneous, ion microprobe studies revealed variations of Ca, Ti, Co, Cr, and Ni near grain edges. These variations were thought to represent diffusion in response to falling temperature of the parent body. Pallasite cooling rates have been estimated based on kamacite taenite textures but results differ by x100. In principle elemental profiles in olivine can allow estimates of cooling rate if diffusion coefficients are known; in addition, given a cooling rate, diffusion coefficients could be derived. Data are presented which show that apparent diffusion profiles can be measured for Al, Ca, Cr, and Mn which qualitatively agree with expected diffusion rates and have the potential of providing independent estimates of pallasite cooling rates.

Zhou, Y.↗
NASA NTRS1992

Olivine in Antarctic micrometeorites - Comparison with other extraterrestrial olivine

The compositions of 5-micron or larger Mg-rich olivines from 26 Antarctic micrometeorite particles were examined and compared with those of other extraterrestrial olivine. The following differences were noted between the Antarctic meteorites and the generally recognized meteorite groups: (1) while refractory-rich (e.g., high Al2O3 or CaO) are common in C2, C3, and UOC meteorites, there are only rare, or possibly no refractory-rich olivines in Antarctic micrometeorites; (2) Mg-rich olivine compositions with FeO less than 1.9 wt pct are underrepresented in the Antarctic micrometeorites, relative to other unequilibrated meteorites; and (3) no Mn-rich, high-Mg olivines were found similar to those described in interplanetary dust, C1, C2, C3, and UOC meteorites.

Steele, Ian M.↗
NASA NTRS1989

Compositions of isolated forsterites in Ornans (C3O)

The Ornans (C3O) carbonaceous chondrite shows many examples of isolated olivine grains which are Mg-rich and show cathodoluminescence (CL). Using backscattered electron imaging to scan and select Mg-rich isolated olivine grains, and a CL detector, the chemical zoning within these grains was investigated together with its relation to CL and to chemical zoning of grains within a Fe-rich chondrule. Composition profiles from the core to the rim of five isolated forsterites showed details of Al, Ca, Sc, Ti, V, Cr, Mn, and Fe zoning with respet ot position and CL color.

Steele, Ian M.↗
NASA NTRS1988

Primitive material surviving in chondrites - Mineral grains

Besides chondrules and various kinds of polymineralic inclusion, carbonaceous chondrites commonly contain, embedded in their matrices, isolated grains of mafic silicates and metallic iron. Most of the silicate grains probably originated in chondrules, but some appear to predate chondrule formation and may have formed as individual grains in the solar nebula. If that was the case, their compositions suggest some departure from equilibrium condensation from a gas of solar composition. Metal-grain compositions are broadly suggestive of nebular formation but the exact nature of the conditions in which they were formed remains problematical.

Steele, Ian M.↗