For part of the human brain, see Amygdala.
Amygdules in lava from Kaiserstuhl in Germany

Amygdules or amygdales (/əˈmɪɡdjuːlz, -deɪlz/) form when the vesicles (pores from gas bubbles in lava) 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.[1] 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.

The word is derived from the Latin word amygdala, meaning "almond tree", and the Greek word αμυγδαλή, meaning "almond" – reflecting the typical shape of an infilled vesicle. Amygdule is more common in American usage, while amygdale is more common in British usage.

See also

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  • Phenocryst – Crystal larger than the rock grains that surround it in an igneous rock
  • Volcanic gas – Gases given off by active volcanoes

References

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  1. ^ Grapes, Rodney H. (2011). Pyrometamorphism (2nd ed.). Berlin, Germany: Springer Verlag. p. 115. ISBN 978-3-642-15587-1.


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Vesicular texture

calcite, quartz, or chalcedony. Individual cavity fillings are termed amygdules (American usage) or amygdales (British usage). Sometimes these can be

Catoctin Formation

within lots of amygdules, chlorite and albite will also form together with albite forming on the rim and chlorite in the center. Amygdules are usually found

Agate

banded chert). Most agates form as nodules within volcanic rock, either as amygdules or thunder eggs. Agates also form in veins within any rock type and in

Glauberite

hydrothermal deposits, as mineral sublimates deposited near fumaroles, in amygdules in basalt, and in nitrate deposits in arid climates. It occurs associated

Chabazite

to the current spelling. Chabazite occurs most commonly in voids and amygdules in basaltic rocks. Chabazite is found in India, Iceland, the Faroe Islands

Purcell Supergroup

chloritized mafic lava flows, pillow basalts, gabbroic sills and dikes; amygdules of quartz, chlorite, and calcite are common. shallow marine 150 m (490 ft)

Aurangabad district, Maharashtra

featuring two distinct layers. The upper layer consists of vesicular and amygdule zeolitic basalt, while the lower layer consists of massive basalt. The

Vug

cluster of deep robin's-egg blue chrysocolla with a covering of drusy quartz Amygdule Rock microstructure Vesicular texture "vug". The Free Dictionary. Farlex