A vesicle in an igneous rock, containing secondary minerals.
- ‘Some consist of pear-shaped segregation vesicles with amygdales at their upper margin.’
- ‘Segregation vesicles are therefore distinguished from amygdales because they are infilled with chilled magma, whereas amygdales represent the infilling of vesicles from post-emplacement fluids.’
- ‘If, after the lava has cooled and set, the vesicles are filled with minerals, they are known as amygdales.’
- ‘Flow margins are often altered, containing abundant epidote and amygdales with quartz, calcite and/or chlorite.’
- ‘Flow tops were avoided as they are almost always riddled with amygdales and show signs of alteration.’
Late 19th century: from French, from Latin amygdala (see amygdala).