Vesicular Basalt

Physical Properties

Hardness: 6-7 on Mohs scale; Color: Dark grey to black groundmass; Luster: Dull/Earthy; Structure: Fine-grained (aphanitic) with visible vesicle holes and small light-colored mineral inclusions; Specific Gravity: 2.8-3.0

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. The holes (vesicles) were formed by gas bubbles trapped in the cooling lava. If the holes are later filled with minerals like quartz or calcite, it is called amygdaloidal basalt.

Uses & Applications

Used primarily in construction as crushed stone, road base, concrete aggregate, and railroad ballast. Highly vesicular specimens are used in landscaping and as 'lava rocks' for grills.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight compared to its size, and the presence of small pits or holes on the surface. Commonly found in volcanic regions such as the Pacific Northwest, Hawaii, and Iceland.

Identified on: 5/19/2026

Mode: Standard