Very-low-grade metamorphism : illite ‘crystallinity’, including inter-laboratory calibration and effect of Na-micas; K-micas as indicators of metamorphic P/T gradients; grade of VLGM in metapelites of HP/LT metamorphic terranes; VLGM in external zones of orogenic belts and in the sedimentary cover of Archaean greenstone belts. X-ray diffraction of phyllosilicates.