Volcanic rock in which rounded cavities formed by expanding gas have subsequently become filled with mineral deposits WordNet 3.0 & Open English WordNet

Amygdules or amygdales form when the vesicles 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. Wikipedia

rock cavity Wikidata

A variety of trap or basaltic rock, containing small cavities, occupied, wholly or in part, by nodules or geodes of different minerals, especially agates, quartz, calcite, and the zeolites. When the imbedded minerals are detached or removed by decomposition, it is porous, like lava. Wiktionary

A rounded mass of secondary mineral found in volcanic rock. Wiktionary

Rounded mass of secondary mineral found in volcanic rock. Wiktionary (translation)