Serpentine
A water-bearing sheet silicate that makes up much of the matrix of CM and CI chondrites.
Key facts
- Formula
- (Mg,Fe)3Si2O5(OH)4
- Family
- Silicates
- Crystal system
- Monoclinic
What it is
Serpentine is a phyllosilicate: a mineral built of sheets of silicon–oxygen groups bonded to sheets of magnesium or iron with hydroxyl. About 13% of its weight is water bound into the structure. It forms when water reacts with olivine and pyroxene at low temperatures.
Where it is found
Fine-grained serpentine is the main mineral of CM chondrites such as Murchison and a major one of CI chondrites and of the Ryugu and Bennu samples. Iron-rich varieties, including cronstedtite, are typical of the least altered CM chondrites. It shows that liquid water flowed through these asteroids within a few million years of their formation.
How it is recognised
In meteorites it is too fine to see except with an electron microscope. Infrared spectra show a strong feature from hydroxyl near 2.7 micrometres, which is also seen on many dark asteroids, linking them to these meteorites.
Did you know?
Spacecraft found the same 2.7-micrometre water signature on Bennu and Ryugu before collecting samples.
When heated, serpentine releases its water; some CM chondrites lost water this way after it formed.