Amygdule

Infilled vesicle in extrusive igneous rock

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. Amygdules usually form after the rock has been emplaced, and are often associated with low-temperature alteration. Amygdules may often be concentrically zoned. Rocks containing amygdules can be described as amygdaloidal.

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