igneous
Beach Pebble (Basalt/Greywacke)
Amygdaloidal Basalt
Hardness: 5-7 Mohs; Color: Dark grey to greenish-grey with fine white veining; Luster: Dull/Sub-vitreous; Texture: Fine-grained (Aphanitic); Shape: Smooth, water-worn (ellipsoidal).
- Hardness
- 5-7 Mohs
- Color
- Dark grey to greenish-grey with fine white veining
- Luster
- Dull/Sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 5-7 Mohs; Color: Dark grey to greenish-grey with fine white veining; Luster: Dull/Sub-vitreous; Texture: Fine-grained (Aphanitic); Shape: Smooth, water-worn (ellipsoidal).
Formation & geological history
Formed through the rapid cooling of basaltic lava. The smooth, rounded shape is a result of mechanical weathering and high-energy water transport on a beach or riverbed over hundreds to thousands of years.
Uses & applications
Commonly used as decorative garden stones, in massage therapy (as hot stones due to high heat retention), and as aggregate in construction.
Geological facts
Beach stones like this often contain tiny veins of quartz or calcite that filled cracks in the rock millions of years ago. Their perfectly smooth texture is a 'natural polish' created by the grinding action of waves and sand.
Field identification & locations
Identify by its heavy weight (high density), dark color, and rounded edges. Common on volcanic coastlines. Collectors look for unique vein patterns or symmetry in the 'tumbled' shape.
