Diabase (Greenstone)

Physical Properties

Hardness: 6-7 (Mohs scale); Color: dark gray, greenish-black, or mottled; Luster: dull to sub-metallic; Crystal structure: phaneritic to aphanitic with ophitic texture; Specific gravity: approx. 3.0

Formation & Geological History

Formed through the cooling of mafic magma in shallow intrusive bodies like dikes or sills. This specific specimen appears water-worn, suggesting a secondary transport process by a river or coastline.

Uses & Applications

Used primarily as crushed stone for construction aggregates, road base, and railroad ballast. Exceptionally durable specimens are used for 'black granite' countertops or monuments.

Geological Facts

Many of the inner stones at Stonehenge are diabase 'bluestones.' It is chemically similar to basalt but has a slightly larger crystal size due to cooling more slowly underground.

Field Identification & Locations

Identify by its heavy weight (high density), dark color, and fine-grained 'salt and pepper' appearance. Common in rift zones and oceanic crust settings.

Identified on: 4/24/2026

Mode: Standard