Basalt, amygdaloidal


Hand Specimen

Fine-grained, greenish black rock comprising dark and white minerals.
Contains amygdales, mostly white, though some have black cores.


Fine-grained plagioclase laths and irregular clinopyroxene (augite) grains, replaced with calcite. Many of the plagioclase laths have been almost entirely altered.

The amygdales are filled with zeolite, growing in spherulitic and radiate patterns. Many have rims of calcite and fine-grained chlorite.

Some vein material - granular quartz with sutured contacts.

Rock History

Fine-grained → rapid, extrusive crystallisation.
Gas bubbles trapped within lava produced vesicles.
Circulation of fluids → precipitation of zeolite within the vesicles.

Advanced Notes

Zeolites are produced at low temperatures. They are commonly precipitated in basaltic volcanic piles.

Rock Name

amygdaloidal basalt

Scale bars

Scale bars in hand specimen photographs represent 1cm.
Scale bars in thin-section photographs represent 1mm.