igneous
Gabbro Pebble (Polished Beach/River Stone)
Gabbro
Hardness: 6-7 on Mohs scale. Color: Mottled dark green, black, and yellowish-tan. Luster: Dull to sub-vitreous. Crystal structure: Phaneritic (coarse-grained intrusive igneous texture). Cleavage: Good in amphibole/pyroxene and feldspar grains. Specific gravity: 2.8 - 3.1.
- Hardness
- 6-7 on Mohs scale
- Color
- Mottled dark green, black, and yellowish-tan
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Mottled dark green, black, and yellowish-tan. Luster: Dull to sub-vitreous. Crystal structure: Phaneritic (coarse-grained intrusive igneous texture). Cleavage: Good in amphibole/pyroxene and feldspar grains. Specific gravity: 2.8 - 3.1.
Formation & geological history
Formed through the slow cooling and crystallization of mafic magma deep within the Earth's oceanic or continental crust. This specific specimen shows significant natural rounding and smoothing from stream or shoreline water erosion.
Uses & applications
Used primarily as decorative pebbles, landscaping stone, crushed stone aggregate, and as polished rock specimens for amateur collections.
Geological facts
Gabbro is the plutonic equivalent of basalt. It forms much of the deep oceanic crust beneath the sea floor.
Field identification & locations
Identified by its salt-and-pepper or mottled dark-and-light coarse-grained texture dominated by dark mafic minerals (pyroxene, amphibole) and plagioclase feldspar. Commonly found along glacial deposits, riverbeds, and ocean beaches worldwide.
