Also found in: Encyclopedia, Wikipedia.
A small gas bubble in igneous, especially volcanic, rock filled with secondary minerals such as zeolite, calcite, or quartz.
[Latin amygdala, almond (from its shape); see amygdala + (nod)ule.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.