New method for exoplanet detection based on iridescence? in Astronomy SE asks about observations of exoplanets, but here I'm asking about our own solar system bodies.

Question: Has opalescence ever been observed on any solar system body besides Earth? Or at least from a sample from one?

Primarily I'm interested in opalescence observed in a spacecraft's data, but observations on Earth from objects from off-Earth (e.g. sample returns, meteorites) are also okay.

Wikipedia's Opalescence begins:

Opalescence refers to the optical phenomena displayed by the mineraloid gemstone opal (hydrated silicon dioxide). However, there are three notable types of opal (precious, common, and fire), each with different optical effects, so the intended meaning varies depending on context. The optical effects seen in various types of opal are a result of refraction (precious and fire) or reflection (common) due to the layering, spacing, and size of the myriad microscopic silicon dioxide spheres and included water (or air) in its physical structure. When the size and spacing of the silica spheres are relatively small, refracted blue-green colors are prevalent; when relatively larger, refracted yellow-orange-red colors are seen; and when larger yet, reflection yields a milky-hazy sheen.

Companion question:

  • 2
    $\begingroup$ Opal has been found in some Martian meteorites, but I don't know if any specimens have it in pieces large enough to see. $\endgroup$ Aug 14, 2021 at 4:06
  • $\begingroup$ True. Opals are known from multiple samples on Mars as I quote. But we may not have been looking for opalescence as such. Opalescence on Earth is known only because we are looking extremely close-up compared with the planetary size scale. $\endgroup$ Jul 24 at 12:55

2 Answers 2


The hydrated silica that produces opalescence is known on Mars. Quoting from. Ref. [1], paragraph 48:

Thus far, hydrated or opaline silica has been found in a wide variety of settings on Mars. On the plains adjacent to Valles Marineris (Ius, Melas, Candor, Ganges, and Juventae Chasmas), opaline silica is exposed in finely layered (meter scale) light‐toned deposits and associated with Fe‐sulfates as well as complex, sometimes inverted channel systems [2; 3; 4]. In Noctis Labyrinthus, opaline silica deposits appear massive [2], while at Mawrth Vallis, hydrated silica is interbedded with both Al-bearing and Fe/Mg-bearing phyllosilicates [5]. Hydrated silica or weakly altered basaltic glass exposures have also been identified in a number of southern highland craters [2], and the Columbia Hills in Gusev crater host opaline silica deposits uncovered by MER Spirit [6; 7].


  1. Kimberly D. Seelos, Raymond E. Arvidson, Bradley L. Jolliff, Steven M. Chemtob (2010). "Silica in a Mars analog environment: Ka’u Desert, Kilauea Volcano, Hawaii". _Journal of Geophysucal Research, 115, E00D15, https://doi.org/10.1029/2009JE003347.

  2. R. E. Milliken et al. (2008). "Opaline silica in young deposits on Mars", Geology 36, 847–850, https://doi.org/10.1130/G24967A.1.

  3. J. L. Bishop et al. (2009). "Mineralogy of Juventae Chasma: Sulfates in the light‐toned mounds, mafic minerals in the bedrock, and hydrated silica and hydroxylated ferric sulfate on the plateau". J. Geophys. Res. 114 E00D09, https://doi.org/10.1029/2009JE003352.

  4. C. M. Weitz, R. E. Milliken, J. A. Grant, A. S. McEwen, R. M. E. Williams, J. L. Bishop, and B. J. Thomson (2010). "Mars Reconnaissance Orbiter observations of light‐toned layered deposits and associated fluvial landforms on the plateaus adjacent to Valles Marineris". Icarus 205, 73– 102, https://doi.org/10.1016/j.icarus.2009.04.017.

  5. N. K. McKeown, J. L. Bishop, E. Z. Noe Dobrea, M. Parente, B. L. Ehlmann, J. F. Mustard, S. L. Murchie, J.‐P. Bibring, and E. Silver (2009). "Characterization of phyllosilicates observed in the central Mawrth Vallis region, Mars, their potential formational processes, and implications for past climate". J. Geophys. Res. 114, E00D10, https://doi.org/10.1029/2008JE003301.

  6. D. W. Ming, et al. (2006). "Geochemical and mineralogical indicators for aqueous processes in the Columbia Hills of Gusev crater, Mars". J. Geophys. Res. 111, E02S12, https://doi.org/10.1029/2005JE002560.

  7. S. W. Squyres, et al. (2008). "Discovery of silica-rich deposits on Mars by the Spirit Rover". Science 320, 1063–1067, https://doi.org/10.1126/science.1155429.

  • $\begingroup$ Cool! They have identified deposits of a mineral on Mars that is associated with opalescence, but I still wonder if they have they observed opalescence? "Has opalescence ever been observed on any solar system body besides Earth? Or at least from a sample from one?" $\endgroup$
    – uhoh
    Jul 24 at 12:31
  • $\begingroup$ A lot depends on whether they are looking for it. They may be more interested in the mineral composition as such. $\endgroup$ Jul 24 at 12:42

As noted,“opalescence” has different definitions in different contexts. Phase reddening has been observed on multiple bodies, such as Mars soil, Bennu regolith, etc, but I’m guessing that’s not what most people associate with the opal gemstones they’ve seen.And there’s the ongoing question of opposition surge, which is ongoing because it’s highly likely multiple effects are going on in multiple situations.


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