The recent paper in Nature The divergent fates of primitive hydrospheric water on Earth and Mars (Nature 552, 391–394 (21 December 2017) doi:10.1038/nature25031) has been linked by many recent news articles. Essentially much of Mars' original surface water may have been incorporated into metamorphic rock, rather than lost to space following the collapse of it's magnetic field then followed by it's atmosphere.

It is suggested that the higher iron content of surface minerals on Mars relative to that of Earth lead to enhanced serpentinization.

I'm having a hard time understanding the use of the term serpentinization as used in the abstract of the Nature paper shown below.

Wikipedia shows a serpentine subgroup of minerals and the mineral serpentinite itself, as well as an image of a rock formation with serpentine patterns.

In this context, does serpentinization just refer to the formation of some hydrated minerals that happen to be of a class that is historically been referred to as serpentinite or it's subgroup, or is serpentinization a process that always produces serpentine patterns?

Despite active transport into Earth’s mantle, water has been present on our planet’s surface for most of geological time. Yet water disappeared from the Martian surface soon after its formation. Although some of the water on Mars was lost to space via photolysis following the collapse of the planet’s magnetic field, the widespread serpentinization of Martian crust suggests that metamorphic hydration reactions played a critical part in the sequestration of the crust. Here we quantify the relative volumes of water that could be removed from each planet’s surface via the burial and metamorphism of hydrated mafic crusts, and calculate mineral transition-induced bulk-density changes at conditions of elevated pressure and temperature for each. The metamorphic mineral assemblages in relatively FeO-rich Martian lavas can hold about 25 per cent more structurally bound water than those in metamorphosed terrestrial basalts, and can retain it at greater depths within Mars. Our calculations suggest that in excess of 9 per cent by volume of the Martian mantle may contain hydrous mineral species as a consequence of surface reactions, compared to about 4 per cent by volume of Earth’s mantle. Furthermore, neither primitive nor evolved hydrated Martian crust show noticeably different bulk densities compared to their anhydrous equivalents, in contrast to hydrous mafic terrestrial crust, which transforms to denser eclogite upon dehydration. This would have allowed efficient overplating and burial of early Martian crust in a stagnant-lid tectonic regime, in which the lithosphere comprised a single tectonic plate, with only the warmer, lower crust involved in mantle convection. This provided an important sink for hydrospheric water and a mechanism for oxidizing the Martian mantle. Conversely, relatively buoyant mafic crust and hotter geothermal gradients on Earth reduced the potential for upper-mantle hydration early in its geological history, leading to water being retained close to its surface, and thus creating conditions conducive for the evolution of complex multicellular life.


does serpentinization just refer to the formation of some hydrated minerals that happen to be of a class that is historically been referred to as serpentinite or it's subgroup

Yes. In simple terms, the reaction is enstatite + forsterite + water = serpentine.

MgSiO3 + Mg2SiO4 + 2H2O = Mg3Si2O5(OH)4

Forsterite and enstatite (or more generally, olivine and pyroxene) are common minerals in mafic igneous rocks. The formation of serpentine locks up water in the resulting solid crystal structure.

You can see more examples of serpentine forming reactions on page 5 of this PDF file.

or is serpentinization a process that always produces serpentine patterns?

No. There is no such thing as "serpentine patterns". The image you link to is of "folded serpentinite". The "serpentinite" bit of it are the green layers, regardless of whether they are folded or not. The nice photogenic folded part is a later tectonic event that is unrelated to the formation of the serpentinite.

  • $\begingroup$ Thank you for adding a simplified, representative reaction (I'm sure it can get complicated) and clarifying my misunderstanding of the use of the word. The linked slides are excellent! $\endgroup$ – uhoh Dec 25 '17 at 12:32
  • $\begingroup$ I've just ran across " serpentinite geology" here: en.wikipedia.org/wiki/Goonhilly_Downs $\endgroup$ – uhoh Feb 24 '18 at 3:55
  • 1
    $\begingroup$ @uhoh yes, there are plenty of serpentinite rocks on Earth. $\endgroup$ – Gimelist Feb 24 '18 at 4:28
  • $\begingroup$ I've now used (okay, copy/pasted) serpinization twice today! 1, 2. Thanks again for the explanation. $\endgroup$ – uhoh Mar 4 '18 at 13:05
  • $\begingroup$ fyi I've just asked How does friction and radiolysis provide hydrogen for “unusual types of methane”? $\endgroup$ – uhoh May 7 at 9:36

Serpentinization is a system of,

chemical reactions which convert anhydrous ferromagnesian silicate minerals (pyroxene, olivine) into hydrous silicate minerals (serpentine) plus some other possibilities like brucite and magnetite. Brucite forms if the precursor rocks are rich in magnesium (dunite, for example). Magnetite forms if there is enough iron present (pyroxenite). Usually serpentinite contains iron in the form of magnetite which gives dark color to serpentinites.

In short, serpenitinization about the formation of hydrated silicate minerals not about the formation of snake (serpent) like skin patterns on rock.

  • $\begingroup$ That was quick, thanks! I'll try to get hold of the article to see how they've identified the minerals from orbit. $\endgroup$ – uhoh Dec 25 '17 at 9:26

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