Same as amygdaloid; specifically, in geology, having a cellular or vesicular structure: said of lava, whether of modern or ancient origin, in which spherical or almond-shaped (whence the name) cavities were formed by the expansion of steam contained in the rocks at the time of its consolidation, and which have later become filled with various minerals, especially quartz, calcite, or the zeolites. The rock having this character is called an amygdaloid, and the cavities themselves, as thus filled by the percolation of heated water through the body of the rock, are called amygdules.