One larger crystal

OlderinteriorYounger rim

The interior can retain evidence of earlier underground storage. Later growth adds an outer record around it.

Separate tiny crystals

Microcrysts

These grains record crystallisation from the final erupted liquid as magma rises and releases gas.

The rock brings these records together. Measuring each component separately helps distinguish earlier storage from the final journey to eruption.

Conceptual cross-sections, not to scale. Texture identifies regions to analyse; chemistry supports their historical interpretation.