Vesicular Basalt with Epidote

Physical Properties

Hardness: 6-7 (Basalt) and 6-7 (Epidote). Color: Dark grey to reddish-brown matrix with lime-green inclusions. Luster: Dull (Matrix) to Vitreous (Epidote). Structure: Vesicular (pitted with gas bubbles). Cleavage: None/Poor.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The green Epidote forms later via hydrothermal alteration of the basaltic minerals in the presence of calcium-rich fluids.

Uses & Applications

Mainly used as a decorative landscaping stone, in construction as aggregate, or as a teaching specimen for geology students.

Geological Facts

The 'bubbles' or vesicles in the rock were created by gas escaping from the lava as it solidified. When these holes are filled with secondary minerals like epidote or quartz, the rock is called an amygdaloidal basalt.

Field Identification & Locations

Identify by finding a dark, heavy rock with small holes (vesicles) and distinct pistachio-green crusts or crystals. Commonly found in volcanic fields, especially in the Lake Superior region or Pacific Northwest.

Identified on: 5/14/2026

Mode: Standard