igneous
Amygdaloidal Basalt
Amygdaloidal Basalt
Hardness (6-7 Mohs), Color: Grayish-green or reddish-brown matrix with light-colored mineral fillings (amygdules), Luster: Dull or earthy matrix with vitreous amygdules, Crystal structure: Aphanitic (fine-grained) matrix.
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Physical properties
Hardness (6-7 Mohs), Color: Grayish-green or reddish-brown matrix with light-colored mineral fillings (amygdules), Luster: Dull or earthy matrix with vitreous amygdules, Crystal structure: Aphanitic (fine-grained) matrix.
Formation & geological history
Formed from the cooling of lava flows where gas bubbles (vesicles) were trapped in the rock and later filled with secondary minerals like quartz, calcite, or zeolites through groundwater infiltration.
Uses & applications
Commonly used in road construction, stone aggregate, and as decorative gravel. Some high-quality specimens with colorful mineral fillings are used as decorative garden stones or for lapidary work.
Geological facts
The name 'amygdule' comes from the Latin word 'amygdala', meaning almond, referring to the almond-shaped mineral fillings. This rock is very common in the Lake Superior region of North America.
Field identification & locations
Identify it by its spotty, polka-dot appearance caused by mineral fillings in a dark volcanic matrix. It is commonly found in ancient volcanic rift zones and along glacial till beaches.
