The myrmekite occurring in acid to basic charnockites of the area around Garbham and Shikaruganji, Srikakulam district, Andhra Pradesh is described. Myrmekite, whenever present, occurs only at the contact of plagioclase and potash feldspar. The textures and paragenesis of minerals suggest that potash feldspar reacted with plagioclase giving rise to myrmekite under favourable stress condition, higher stress favouring the formation of myrmekite. The difference in the stress factor or the microstrain pattern in the rock can explain the presence of myrmekite at some contacts of plagioclase–potash feldspar and absence in others.

Large ignimbrite dykes continuous with an overlying sheet of rhyolitic ignimbrite have been found at two localities in the centrally-subsided block of the Sabaloka cauldron. There is good evidence that these dykes fed ash-flow eruptions. Other possible feeder vents occur along the marginal fracture zone of the cauldron but evidence for the origin of some of these structures is ambiguous. Ignimbrites within the dyke-shaped feeders contain a very strong eutaxitic foliation oriented parallel to the contacts and this feature is thought to result from inwardly-directed pressures exerted by the dyke walls during a collapse which followed eruption of the ash-flows. Vents of this type are believed to originate by permissive intrusion through the roof of a shallow-seated magma chamber, in contrast to forcefully injected diatreme vents. A broad genetic classification of these bodies is suggested, based on their mode of emplacement.

The cordierite–sillimanite rocks first reported from Joan Lake Area, Labrador, show some unusual mineral associations and textures. Two myremkitic intergrowths, one among cordierite, potash feldspar and quartz, and the other between potash feldspar and plagioclase feldspar, are observed. The presence of microcline–microperthite and the textures described in the sequel indicate that these rocks were recrystallized at high temperature.