What is "poikilitic"

Poecilitic \P[oe]`ci*lit"ic\, a. [Gr. poiki`los many-colored, variegated.] (Geol.)

1. Mottled with various colors; variegated; spotted; -- said of certain rocks.

2. Specifically: Of or pertaining to, or characterizing, Triassic and Permian sandstones of red and other colors.

a. (context geology English) Describing the texture of an igneous rock that has small crystals of one mineral scattered among larger crystals of another

Poikilitic texture refers to igneous rocks where large component crystals contain smaller crystals of other minerals within them. In poikilitic rocks, the contained smaller crystals are termed 'chadacrysts' and the larger phenocrysts are termed 'oikocrysts'. A poikilitic texture is most easily observed in petrographic thin sections.

In some rocks there seem to be little tendency for the minerals to envelop one another. This is true of many gabbros, aplites and granites. The grains then lie side by side, with the faces of the latter moulded on or adapted to the more perfect crystalline outlines of the earlier.

When the smaller idiomorphic crystals of the first-formed are scattered irregularly through the larger and less perfect crystals of later origin, the structure is said to be poikilitic.

A poikioblast is a larger crystal that contains smaller crystals of other minerals. Poikioblasts are a texture of metamorphic rocks.

Poikilitic texture describes the occurrence of one mineral that is irregularly scattered as diversely oriented crystals within much larger host crystals of another mineral.