Amygdules form when the vesicular cavities (created by expanding gas bubbles in volcanic lava) are filled with a secondary mineral such as calcite, quartz, or one of the zeolites, which are deposited by having minerals "wash" through the pores in the rock (see Porosity/Permeability). They are filled from the outside, making the amygdules concentrically layered. Vesicular texture is a volcanic rock texture characterised by, or containing, many vesicles. ... This article is about volcanoes in geology. ... Look up lava, Aa, and pahoehoe in Wiktionary, the free dictionary. ... This article is about minerals in the geologic sense; for nutrient minerals see dietary mineral; for the band see Mineral (band). ... Doubly refracting Calcite from Iceberg claim, Dixon, New Mexico. ... Quartz is the most abundant mineral in the Earths continental crust. ... Zeolite Zeolites (Greek, zein,to boil;lithos,a stone) are minerals that have a porous structure. ...

"Amygdules" refer to the smaller ones. "Amygdales" refer to the larger ones.