Abstract: Transmission electron microscopy shows that normal chrysotile and polygonal serpentine occur together and in parallel association with balangeroite, within the slip-veins of the Balangero serpentinite. Chrysotile substitutes for balangeroite and it is later replaced by the polygonal serpentine.

The chrysotile fibres are packed together according to a rod close-packing scheme, with defects. Lattice images of the polygonal serpentine confirm the structure model proposed by Middleton and Whittaker (1976), consisting of polygonally arranged fiat layers. This structural type is probably common for serpentine minerals and constitutes a fourth main type of layer configuration in 1:1 layer silicates.