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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Co(PO2)2 by Materials Project

Co(PO2)2 crystallizes in the monoclinic P2/c space group. The structure is two-dimensional and consists of one Co(PO2)2 sheet oriented in the (0, 1, 0) direction. Co4+ is bonded to six O2- atoms to form edge-sharing CoO6 octahedra. There are a spread of Co–O bond distances ranging from 2.01–2.28 Å. There are two inequivalent P2+ sites. In the first P2+ site, P2+ is bonded in a bent 120 degrees geometry to two equivalent O2- atoms. Both P–O bond lengths are 1.53 Å. In the second P2+ site, P2+ is bonded in a water-like geometry to two equivalent O2- atoms. Both P–O bond lengths are 1.54 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to two equivalent Co4+ and one P2+ atom. In the second O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Co4+ and one P2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Co(PO2)2 by Materials Project

Co(PO2)2 crystallizes in the orthorhombic Pmma space group. The structure is two-dimensional and consists of one Co(PO2)2 sheet oriented in the (0, 0, 1) direction. Co4+ is bonded to six O2- atoms to form edge-sharing CoO6 octahedra. There are two shorter (2.01 Å) and four longer (2.21 Å) Co–O bond lengths. There are two inequivalent P2+ sites. In the first P2+ site, P2+ is bonded in a bent 120 degrees geometry to two equivalent O2- atoms. Both P–O bond lengths are 1.53 Å. In the second P2+ site, P2+ is bonded in a water-like geometry to two equivalent O2- atoms. Both P–O bond lengths are 1.54 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Co4+ and one P2+ atom. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to two equivalent Co4+ and one P2+ atom.

36 MATERIALS SCIENCE↗
NASA NTRS2000

Geology and geochemistry of paleosols developed on the Hekpoort Basalt, Pretoria Group, South Africa

The Hekpoort paleosols comprise a regional paleoweathering horizon developed on 2.224 +/- 0.021 Ga basaltic andesite lavas at the top of the Hekpoort Formation of the Pretoria Group, Transvaal Supergroup, South Africa. In five separate profiles, from outcrops along road cuts near Waterval Onder and the Daspoort Tunnel and in three drill cores from the Bank Break Area (BB3, BB8, and BB14), the top of the paleosol is a sericite-rich zone. The sericite zone grades downward into a chlorite-rich zone. In core BB8 and in the road cut at the Daspoort Tunnel, we sampled the underlying or parent basaltic andesite into which the chlorite zone grades. We did not obtain samples of the parent material at Waterval Onder and in cores BB3 and BB14, but chemical analyses indicate that the chlorite and sericite zones in these profiles derive from underlying lavas similar to the ones we sampled in core BB8 and at the Daspoort Tunnel. The presence of apparent rip-up clasts of the paleosol in the overlying ironstones of the Strubenkop Formation in the cores from Bank Break makes it very unlikely that most of the alteration was a result of interactions with hydrothermal fluids. Desiccation cracks at the top of the paleosol that were filled with sand during the deposition of the overlying sediments at Waterval Onder point to a subaerial weathering origin. Very little, if any, Al, Ti, Zr, V, or Cr moved a discernible distance during weathering of any of the five profiles. The vertical distribution of Fe, Mg, Mn, Ni, and Co indicates that these elements were largely removed from the top of the soil during weathering. The overall abundance of these elements in each of the profiles indicates that a significant fraction of the complement lost from the top subsequently reprecipitated in the lower portion of the soil as constituents of an Fe2(+) -rich smectite. The loss of Fe from the top of the soil during weathering of the Hekpoort paleosols indicates that atmospheric PO2 was less than 8 x 10(-4) atm about 2.22 Ga. Fe2(+) -rich smectite should only precipitate during soil formation if atmospheric PCO2 is less than or equal to 2 x 10(-2) atm (Rye, Kuo, and Holland, 1995). Ca and Na were largely lost during weathering. Some Na was apparently added to the sericite zone in cores BB3, BB8, and BB14 after weathering. All five profiles are enriched in K and Rb, and most are enriched in Ba. The distribution of these elements indicates that they all were added during post-weathering hydrothermal metasomatism. Rb-Sr analysis of the paleosol at the Daspoort Tunnel indicates that metasomatism last affected that profile 1.925 +/- 0.032 Ga (Macfarlane and Holland, 1991).

Non-NASA Center↗