igneous
Beach Pebble (Gabbro or Basalt Porphyry)
Mafic Igneous Rock (Porphyritic Basalt / Gabbro)
Hardness: 6-7 on Mohs scale. Color: Dark grey to blackish matrix with lighter feldspar inclusions. Luster: Dull to sub-vitreous. Texture: Water-worn, smooth, oval beach pebble with porphyritic/phaneritic texture. Specific gravity: ~2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Dark grey to blackish matrix with lighter feldspar inclusions. Luster: Dull to sub-vitreous. Texture: Water-worn, smooth, oval beach pebble with porphyritic/phaneritic texture. Specific gravity: ~2.8-3.0.
Formation & geological history
Formed from the cooling of mafic silicate lava or magma rich in magnesium and iron. The smooth, rounded shape is created through mechanical weathering and coastal wave abrasion over thousands of years.
Uses & applications
Used primarily for landscaping, aquariums, decorative pebble tile, and as general beach stones for casual rock collecting.
Geological facts
Beach pebbles like this are natural indicators of coastal erosion and longshore drift. Over extensive time periods, rough angular rock fragments are rounded through perpetual grinding against sand and water.
Field identification & locations
Identified by its water-rounded oval shape, dense dark mafic mineral base, and mottled pale plagioclase feldspar grains. Commonly found on cobble beaches, coastal river outlets, and gravel deposits worldwide.
