Fig. 5 Scanning electron microscopy photomicrographs. Pseudomorphs after biotite in M2 saprolite. (1) Weathering products in coating and interlayer sites. (2) Prismatic weathering products in coating site. (3) Topotaxial tubular halloysite developing at edges of biotite 001 planes. (4) Kaolinite–gibbsite pseudomorph after biotite