These crystals form during an earlier phase of magmatic activity and are later incorporated into a newer batch of magma. Unlike crystals that grow directly from the final melt, they carry chemical signatures of the deeper, older plumbing system. Geologists analyze them to reconstruct the timeline and evolution of volcanic systems before an eruption.
Heard on the job
The zircon populations show a mix of autocrysts and older antecrysts scavenged from the lower crustal mush.
Insider tip
Identifying these crystals is critical when dating volcanic rocks, as their older isotopic ages can skew the calculated age of the actual eruption.
Do not mix it up with
- Autocryst: An autocryst crystallizes directly from the host magma, whereas an antecryst forms in an earlier magmatic pulse and is later entrained.