poikilitic

Poikilitic describes a textural relationship in igneous and metamorphic rocks where larger crystals, called poikiloblasts, enclose numerous smaller crystals of another mineral. These smaller crystals are referred to as inclusions. The poikilitic texture is a result of crystal growth occurring at a rate faster than the diffusion of the enclosed minerals. This can happen when a new mineral grows in a rock that has already crystallized, or when rapid cooling prevents inclusions from being incorporated into the growing crystal lattice. The larger crystal essentially "sweeps up" the smaller ones as it grows.

This texture is common in various rock types. For instance, in some granites, large K-feldspar crystals may enclose smaller quartz and plagioclase grains. In metamorphic rocks, large staurolite or garnet crystals can enclose smaller quartz, micas, or feldspars. The specific minerals involved and their arrangement within the poikiloblast can provide clues about the conditions of formation, such as temperature, pressure, and the availability of different chemical elements. The size and abundance of the inclusions can vary significantly, from a few scattered grains to a dense, pervasive network within the larger crystal. The term poikilitic is derived from the Greek words "poikilos" meaning varied or manifold, and "lithos" meaning stone.