Unit Cell
The unit cell has six manganese Mn4+ sites and twelve oxygen O2- sites constituting the octahedral framework. Mg and Al may substitute for Mn, and the tunnels contain large cations and water molecules.
There is one formula unit per unit cell (Z = 1). The side lengths are a = 9.8 Å, b = 2.8 Å and c = 9.6 Å, with angle β = 94.1°. More detailed values given in the references are:
-
- a = 9.764 Å, b = 2.842 Å, c = 9.551 Å, β = 94.14°
- a = 9.7570(15) Å, b = 2.8419(5) Å, c = 9.5684(14) Å, β = 94.074(14)°
- a = 9.75 Å, b = 2.849 Å, c = 9.59 Å β = 90°
Varieties also occur with a = 14.6 Å and a = 24.38 Å, having the same b and c values as above.
Intergrowths of elongated crystallites resembling the twinned variety of acicular rutile have been observed by electron microscopy in todorokites from an iron-manganese concretion from the Pacific Ocean (a = 14.6 Å) and from the Bakal deposit (a = 14.6 Å and 24.4 Å). Todorokites with a around 25 Å have been found in samples from Sterling Hill and the Takhte-Karacha deposit.
Read more about this topic: Todorokite
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