On the question of origin of the columnar separately in the basalts and its analogs

Columnar jointing - a unique texture formation of stone columns up to 10 m, mostly hexagonal cross section. It is typical for rocks of basic composition. There are several points of view on the origin of columnar separately. Most researchers explain their origin as the effect of contraction forces in the cooling lava. Contraction hypothesis has several disadvantages. It cannot explain the differentiation of matter inside the each «pillar». We propose a model of convection-contraction, which accurately reflects the characteristics of the process. It is emphasized that at the initial stage of the process the convective flow of lava material is dominated.