Antecrysts

Antecrysts are crystals that crystallized from the same magmatic system as the host crystal, but at an earlier stage of crystallization. They are distinct from phenocrysts, which formed together with the host during the same crystallization event, and from xenocrysts, which originate outside the current magmatic system (for example, from surrounding country rock) and were incorporated without forming from the present melt.

Antecrysts form when a magma remains in a chamber long enough to develop additional crystals, or when recharge and differentiation events alter the melt composition. Crystals that formed earlier in the same magmatic history can be incorporated into later crystals or trapped as inclusions within growing crystals. As a result, antecrysts record a protracted or cyclical crystallization history within a single magmatic system rather than an external origin.

In practice, antecrysts are used to interpret magmatic processes such as extended crystallization, magma mixing, and recharge episodes. Minerals commonly acting as antecrysts include plagioclase and other minerals that show chemical or textural evidence of an earlier crystallization stage yet remain chemically related to the host melt. Identifying antecrysts involves recognizing chemical affinities and zoning patterns that link them to the same magmatic source while distinguishing them from xenocrysts and primary phenocrysts.

See also: xenocryst, phenocryst, cumulate, magmatic differentiation.