L161 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.

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

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