Amygdule

Amygdules or amygdales (/əˈmɪɡdjuːlz, -deɪlz/) form when the vesicles (pores from gas bubbles in lava) of a volcanic rock or other extrusive igneous rock are infilled with a secondary mineral, such as calcite, quartz, chlorite, or one of the zeolites.

[1] Amygdules usually form after the rock has been emplaced, and are often associated with low-temperature alteration.

The word is derived from the Latin word amygdala, meaning "almond tree", and the Greek word αμυγδαλή, meaning "almond" – reflecting the typical shape of an infilled vesicle.

Amygdule is more common in American usage, while amygdale is more common in British usage.

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