Vesicular Basalt with Quartz/Chalcedony

Physical Properties

Hardness: 6-7 (Basalt) and 7 (Quartz); Color: Dark grey to black with translucent white/grey patches; Luster: Dull to vitreous; Crystal structure: Aphanitic (fine-grained) with amorphous or microcrystalline silica; Cleavage: None/Conchoidal.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The holes (vesicles) are created by trapped gas bubbles during solidification. Secondary mineral deposition (the lighter portion) occurs when silica-rich fluids permeate the rock over geological timescales.

Uses & Applications

Commonly used in construction as aggregate, in landscaping, and sometimes for 'lava rock' in grills or filtration. Small unique specimens are decorative and used in educational rock kits.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The moon's 'maria' (dark plains) are also composed of basalt.

Field Identification & Locations

Identify by its dark color, heavy weight (high specific gravity), and the presence of small holes or pits. It is commonly found in volcanic regions, such as Hawaii, Iceland, and the Pacific Northwest.

Identified on: 4/18/2026

Mode: Standard