Vesicular Basalt River Cobble

Hardness: 5-6 Mohs. Color: Grey to dark grey. Luster: Dull/Earthy. Structure: Aphanitic (fine-grained) with vesicular texture (pitted). Specific gravity: 2.8-3.0.

Formed from rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The pits (vesicles) were formed by gas bubbles trapped in the cooling lava. These specimens in the Stura di Demonte river originated in the Alpine volcanic or ophiolitic complexes.

Commonly used in construction as aggregate, for road base, or in landscaping. High-quality vesicular rocks are sometimes used as pumice stones for abrasion.

This specimen is a well-rounded river cobble, indicating it has been transported a long distance by water from the mountains, which smoothed its edges while preserving the gas-bubble pits.

Identify by its heavy weight relative to size (high density) and the presence of small spherical or irregular holes on a dark, fine-grained surface. Found frequently in riverbeds draining the Western Alps.