Hematite Marbles

Hematite concretions known from Earth (e.g. Utah, Fig. 1a) usually form by subsurface precipitation in flowing water. Marble-shaped pebbles ("Blueberries", Fig. 1b) were also discovered on Mars by the Mars Exploration Rover Opportunity.

Figure 1 a/b: "Blueberries": Hematite concretions found on the Martian surface at Meridiani Planum [Catling, 2004]; NASA/JPL/Cornell (left). Hematite marbles found in Utah/ Monument Valley [Chan et al., 2004] (right).

Hematite (Fe2O3) is a mineral that in most cases requires water for its formation, but it can also result form a dry, thermal oxidation process. For Meridiani Planum a formation by water is assumed [Hynek et al., 2002]. The presence of water in turn is linked to life. Therefore hematite indicates wetter and warmer conditions on Mars in time of hematite formation.

There are many explanations of how the hematite in Meridiani was formed [Chan et al., 2004]:

  • precipitation in large lakes or hot springs (during ancient Tharsis volcanism)
  • residue when water leached away other minerals
  • chemical alteration of volcanic ash deposits

On Mars hematite appears as spherules on surface layers and in shallow depressions (Fig. 2). The "grain" size is comparable to small blueberries (< 0.5 cm) [Chan et al., 2004] and the iron source is supposed basaltic (> 80 % [Christensen et al., 2001] or andesitic [Bandfield et al., 2000]. The Martian hematite is a grey crystalline hematite [Christensen et al., 2000a; Christensen et al., 2000b; Christensen et al., 2001; Hynek et al., 2002; Catling and Moore, 2003; Christensen and Ruff, 2004; Ormö et al., 2004; Glotch et al., 2006], a pure hematite having a larger crystal structure than the reddish iron oxide known as rust. It formed as a secondary hematite out of Fe-rich strata in an acidic groundwater influenced environment [Hynek et al., 2002].

Figure 2: Hematite nodules in Endurance crater detected by MER Opportunity (image: NASA/JPL/Cornell).

On Earth they are also accumulated on surface layers and in topographic lows as spherules or other shapes (depending on the host texture) on the scale of 1-20 cm in diameter. In Utah the host rock is a sandstone (fine- to medium-grained quartz arenite) cemented by hematite making up a few percent of the rock [Chan et al. 2000]. The iron source is hematite grain coatings. Hydrocarbon-rich, brine-influenced fluids were mixed with oxygen-rich groundwater circulating through this permeable rock. Chemical reactions then made the minerals precipitate to form layered spherical pebbles. The surrounding Jurassic Navajo sandstone was eroded with time and the hard resistant concretions accumulated on the ground (Fig. 3).

Figure 3: Hematite marbles exposed in Grand Staircase-Escalante National Monument in southern Utah (image: B. Bowen).

References

  • Bandfield, J. L. , V. E. Hamilton, and P. R. Christensen (2000): A Global View of Martian Surface Compositions from MGS-TES, Science, 287, 1626-1630.
  • Catling, D. C. and J. M. Moore (2003): The nature of coarse-grained crystalline hematite and its implications for the early environment of Mars, Icarus, 165, 277-300.
  • Catling, D. C. (2004): On Earth, as it is on Mars, Nature, 429 (6), 707-708.
  • Chan, M. A., W. T. Parry, and J. R. Bowman (2000): Diagenetic Hematite and Manganese Oxides and Fault-Related Fluid Flow in Jurassic Sandstones, Southeastern Utah, AAPG Bulletin, 84, 1281-1310.
  • Chan, M. A., Brenda Beitler, W. T. Parry, J. Ormö, and G. Komatsu (2004): A possible terrestrial analogue for haematite concretions on Mars, Nature, 429, 731-734.
  • Christensen, P. , M. Malin, D. Morris, J. Bandfield, M. Lane, and K. Edgett (2000a): The Distribution of Crystalline Hematite on Mars from the Thermal Emission Spectrometer: Evidence for Liquid Water, Lunar and Planetary Institute Conference Abstracts, March 1, 2000.
  • Christensen, P. R., R. V. Morris, M. D. Lane, J. L. Bandfield, and M. C. Malin (2001): Global mapping of Martian hematite mineral deposits: Remnants of water-driven processes on early Mars, JGR, 106 (E10), 23,873-823,885.
  • Christensen, P. R. and S. W. Ruff (2004): Formation of the hematite-bearing unit in Meridiani Planum: Evidence for deposition in standing water, JGR, 109.
  • Christensen, P. R. , J. L. Bandfield, R. N. Clark, K. S. Edgett, V. E. Hamilton, T. Hoefen, H. H. Kieffer, R. O. Kuzmin, M. D. Lane, M. C. Malin, R. V. Morris, J. C. Pearl, R. Pearson, T. L. Roush, S. W. Ruff, and M. D. Smith (2000b): Detection of crystalline hematite mineralization on Mars by the Thermal Emission Spectrometer: Evidence for near-surface water, Journal of Geophysical Research, 105, 9623-9642.
  • Glotch, T. D., J. L. Bandfield, P. R. Christensen, W. M. Calvin, S. M. McLennan, B. C. Clark, A. D. Rogers, and S. W. Squyres (2006): Mineralogy of the light-toned outcrop at Meridiani Planum as seen by the Miniature Thermal Emission Spectrometer and implications for its formation, JGR, 111.
  • Hynek, B. M., R. E. Arvidson, and R. J. Phillips (2002): Geologic setting and origin of Terra Meridiani hematite deposit on Mars, JGR, 107.
  • Ormö, J., G. Komatsu, M. A. Chan, B. Beitler, and W. T. Parry (2004): Geological features indicative of processes related to the hematite formation in Meridiani Planum and Aram Chaos, Mars: a comparison with diagenetic hematite deposits in southern Utah, USA, Icarus, 171, 295-316.

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Last update: 07/06/2010 14:41