cumulate

In geology, cumulates are rocks formed from the segregation of minerals during the cooling and crystallization of magma. Magma, which is molten rock, can produce diverse assemblages of cumulates even if it starts as a uniform liquid. These rocks are typically found in mafic and ultramafic igneous rocks, which have low silica content.1

The formation of cumulates is influenced by the viscosity of the magma; lower viscosity magmas allow mineral grains to move more freely, facilitating segregation before crystallization is complete. While sinking of dense minerals was a long-held theory, current understanding suggests that in-place crystallization and density currents within magma chambers play more significant roles in forming magmatic cumulates. Key ore minerals that form as magmatic cumulates include chromite, magnetite, and ilmenite.1