Abstract

In an attempt to obtain information about garnet nucleation a series of eleven apparently homogeneous metamorphic rocks, from a small area near Mallaig, Inverness, Scotland, have been analysed to determine bulk chemical and modal compositions, garnet grain size and number of garnet crystals occurring in unit volume of rock (N). No correlation of N with any function of chemical and modal compositions could be found, and it is therefore concluded that, if the influence of trace components can be neglected, externally imposed factors (for example, time-temperature variation) or internal physical factors (for example, the surface area of the rock just prior to garnet formation) must exert a controlling influence on garnet nucleation. It was found, however, that in each specimen, there was a preferred crystal radius and the relative frequency of occurrence about this preferred value was constant for all samples studied. Preliminary comparison with other systems suggested that the nature of this relationship may provide evidence of the conditions under which these rocks recrystallized.

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