Amygdules or amygdales form when the gas bubbles or vesicles in volcanic lava (or other extrusive igneous rocks) are infilled with a secondary mineral such as calcite, quartz, chlorite or one of the zeolites. Amygdules usually form after the rock has been emplaced, and are often associated with low-temperature alteration.

Amygdule
amygdule
Amygdule
Amygdule mineral zoning in the Portage Lake Lava series, Michigan Copper District
Non-coaxial horizontal shortening strains preserved in twinned amygdule calcite, DSDP hole 433, Suiko seamount, northwest pacific pl...
Platinum-group mineral occurrence associated with flow top amygdule sulfides in komatiitic basalt, Abitibi Greenstone Belt, Ontario
Amygdule Minerals in Keweenawan Basalt, South Range Quarry, Douglas County, Wisconsin
(Table 2) Relative abundances of secondary minerals forming amygdule and fracture fillings in altered basalts at DSDP Holes 92-597B ...
Diagenesis of intermediate and mafic volcanic rocks of Yingcheng Formation (K1y) in the Songliao basin: Sequential crystallization, ...
High-resolution X-ray imaging of amygdules for measuring bubble size distribution in ancient lava flows
amygdale - Springer
Word to the Wise
Corrensite and mixed-layer chlorite/corrensite in metabasalt from northern Taiwan: TEM/AEM, EMPA, XRD, and optical studies