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Name used for a large group of phyllosilicate minerals with the generalized formula X2-3 Y2 O5 (OH)4. Due to their various structures (meteoritics focuses primarily on (Fe, Mg)3Si2O5(OH)4), serpentine can be used to understand the chemistry and progress of aqueous alteration (hydration) of olivine, amphibole, or pyroxene dating back to the formation of the solar system. The hydration process is called “serpentinization”. When serpentinization occurs with other geochemical mechanisms, the process can produce a broad range of abiotic organic compounds, such as CH4 (methane). Serpentine can be found in a few various meteorite types, but is by far most prevalent in CM carbonaceous chondrites. However, it has also been found in some Martian nakhlites as well. Serpentine and its group of associated minerals form at relatively low temperatures as low as ~300 K and can remain thermally stable to ~900 K (depending on conditions). The presence of serpentine is one indicator that a meteorite has undergone alteration in the presence of water. The presence of carbonates is another1.

The three mineral polymorphs of serpentine are antigorite and lizardite, which occur as massive aggregations, and chrysotile, which is fibrous. Chrysotile is one of the main forms of asbestos. A misfit between the octahedral and tetrahedral sheets causes bending, which is distributed into corrugations in antigorite and causes chrysotile to curl into cylindrical (often hollow) tubes. The idealized formula of these three polymorphs is Mg3(Si2O5)(OH)4, although in nature some of the magnesium ions are typically replaced by iron or other cations. Most serpentine in CM chondrite matrices appear to be Fe-bearing chrysotile and current research suggests that chrysotile growth is favored in fluid-filled voids. Even within the same CM meteorite, the various regions of serpentine can exhibit a very wide range Mg-Fe substitution.

The composition of serpentine is very uniform. The most important substitution is Fe2+ ↔ Mg2+ ↔ Ni2+ with a much less important substitution of Al3+ ↔ Si4+. Chrysotile shows least chemical deviation from ideal composition.


Note: Brucite is the mineral form of magnesium hydroxide, with the chemical formula Mg(OH)2. Image Source: Unknown







When most of the Mg is replaced by Fe, the resulting mineral is called cronstedtite or sometimes referred to as Fe-rich serpentine. Cronstedtite is another major constituent of CM chondrites. Note that cronstedtite is not a pure endmember but always contains some Mg in solid solution.

Additional reading:

  1. Serpentinite:What, Why, Where?
  2. Ferric saponite and serpentine in the nakhlite martian meteorites
  3. Lizardite versus antigorite serpentinite: Magnetite, hydrogen, and life(?)
  4. Serpentinization and the Formation of H2 and CH4 on Celestial Bodies (Planets, Moons, Comets)


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