Igneous
Amygdaloidal Basalt
Amygdaloidal Basalt
Dark grey to greenish groundmass (fine-grained) with white or light-colored amygdules (filled vesicles) which are often quartz, calcite, or zeolites. Hardness varies depending on the specific minerals present, but the basaltic matrix is around 5.5-6 on the Mohs scale.
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark grey to greenish groundmass (fine-grained) with white or light-colored amygdules (filled vesicles) which are often quartz, calcite, or zeolites. Hardness varies depending on the specific minerals present, but the basaltic matrix is around 5.5-6 on the Mohs scale.
Formation & geological history
Forms from the cooling of lava flows. Gas bubbles (vesicles) are trapped in the cooling lava. Later, mineral-rich fluids percolate through the rock, depositing secondary minerals in the vesicles, forming amygdules.
Uses & applications
Generally used as crushed stone for construction, road base, and railroad ballast. Uniquely formed pieces might be collected.
Geological facts
The word 'amygdaloidal' comes from the Greek word for 'almond', referring to the typical shape of the filled vesicles.
Field identification & locations
Identified by the dark, fine-grained matrix with distinct, often rounded or almond-shaped, lighter-colored mineral inclusions. Commonly found in regions with historical volcanic activity.
