igneous
River Pebble (Gabbro or Dark Sandstone variety)
Mafic Intrusive Rock (Plagioclase Feldspar and Pyroxene)
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black with light speckles; Luster: Dull (weathered); Crystal structure: Phaneritic (visible grains); Cleavage: Poor; Specific Gravity: 2.7-3.3
- Hardness
- 6-7 Mohs
- Color
- Dark grey to greenish-black with light speckles
- Luster
- Dull (weathered)
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to greenish-black with light speckles; Luster: Dull (weathered); Crystal structure: Phaneritic (visible grains); Cleavage: Poor; Specific Gravity: 2.7-3.3
Formation & geological history
Formed from the slow cooling of magnesium and iron-rich magma beneath the Earth's surface. This specimen has been rounded and smoothed by water transport in a river or stream environment.
Uses & applications
Commonly used as decorative landscaping stone, drainage aggregate, and in construction as road base or concrete filler.
Geological facts
River pebbles like this one are nature's 'tumblers.' The rounded shape indicates long-distance travel from its original source, often over hundreds of miles in high-energy water environments.
Field identification & locations
Identify in the field by its smoothed, rounded edges and phaneritic (granular) texture. It is extremely common in riverbeds and coastal areas globally.
