Cronstedtite
An iron-rich serpentine mineral typical of the least altered CM chondrites.
Key facts
- Formula
- Fe3(Si,Fe)2O5(OH)4
- Family
- Silicates
- Crystal system
- Monoclinic or trigonal
What it is
Cronstedtite is a member of the serpentine group in which iron, partly oxidised, replaces most of the magnesium and some of the silicon. It forms when water reacts with iron-rich materials, including metal. It is named after Axel Fredrik Cronstedt, the Swedish chemist who discovered nickel.
Where it is found
It is abundant in the matrix and in alteration rims of CM chondrites such as Murchison and Cold Bokkeveld. As alteration went further, it was replaced by more magnesium-rich serpentine, so the amount of cronstedtite helps measure how far water altered a CM chondrite.
How it is recognised
It is black and very fine-grained in meteorites, usually identified by X-ray diffraction or electron microscopy. In a few meteorites it forms crystals large enough to be visible under the microscope.
Did you know?
Cronstedtite is one of the first minerals to form as water attacks metal in CM chondrites.
Its crystal layers can stack in more than ten different patterns.