intergrown

Intergrown is an adjective used in mineralogy and geology to describe two or more mineral species or crystallites that have grown together in direct contact, such that the boundaries between them are internal and the grains appear as a single composite entity. In an intergrown texture, the crystal lattices of the constituent minerals meet along interfaces, and the grains cannot be separated without damaging one or both minerals. Intergrowth can occur during simultaneous crystallization from a melt or solution, or during metamorphic or hydrothermal growth when space and chemical conditions favor parallel or sequential overgrowth.

Intergrowth is common in many rock types and textures, including metamorphic rocks and hydrothermal ore deposits. It can produce mosaic or interpenetrating textures, where the two minerals form complex interlocking shapes. Epitaxial intergrowth occurs when the overgrowing mineral maintains a crystallographic relationship to the substrate, while non-epitaxial intergrowth lacks a fixed orientation between phases.

Intergrowth is distinguished from exsolution textures, in which a single mineral solubility system separates into two distinct phases upon cooling, often forming lamellae or ribbons within a grain rather than true intergrown grains.

Identification of intergrown textures relies on microscopy and microanalysis. Polarized light microscopy can reveal distinct phase boundaries, while scanning electron microscopy and electron microprobe analysis can determine the mineral phases present. Intergrowth textures provide clues about the crystallization environment, including temperature, pressure, and chemical conditions, and they can influence the interpretation of mineral modal abundances and the mechanical properties of rocks.