Basalt with Amygdaloidal Inclusions

Physical Properties

Hardness: 6 (Mohs scale); Color: dark grey to black with green/white inclusions; Luster: dull to earthy; Structure: fine-grained (aphanitic) with vesicular/amygdaloidal pockets; 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 visible pits or filled spots (amygdules) represent gas bubbles that were later filled with minerals like quartz, calcite, or zeolites.

Uses & Applications

Commonly used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Decorative specimens are used in landscaping and mineral collecting.

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. Amygdaloidal basalt specifically indicates a history of secondary mineral deposition via hydrothermal fluids.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and the presence of tiny holes or mineral-filled circles. Commonly found in volcanic regions such as the Pacific Northwest, Hawaii, or the Deccan Traps.

Identified on: 4/29/2026

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