igneous
Gabbro (Water-worn Pebble)
Gabbro
Hardness: 6-6.5 on Mohs scale. Color: Dark gray, greenish-black, speckled with lighter plagioclase feldspar. Luster: Sub-vitreous to dull (weathered pebble surface). Texture: Medium- to coarse-grained phaneritic intrusive igneous texture.
- Hardness
- 6-6
- Luster
- Sub-vitreous to dull (weathered pebble surface)
Identified More igneous →
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Physical properties
Hardness: 6-6.5 on Mohs scale. Color: Dark gray, greenish-black, speckled with lighter plagioclase feldspar. Luster: Sub-vitreous to dull (weathered pebble surface). Texture: Medium- to coarse-grained phaneritic intrusive igneous texture.
Formation & geological history
Formed from the slow cooling and crystallization of mafic magma deep within the Earth's oceanic or continental crust. Often eroded into rounded pebbles by river or wave action.
Uses & applications
Used in crushed stone for construction, road base, concrete aggregate, and dimension stone (often sold commercially as 'black granite'). Also collected as beach or river rocks.
Geological facts
Gabbro is the intrusive chemical equivalent of basalt. It makes up a significant portion of the Earth's oceanic crust beneath the thin layer of basalt.
Field identification & locations
Identified by its dark, coarse-grained, interlocking mineral crystals (mainly pyroxene and calcium-rich plagioclase). Frequently found on ocean beaches, riverbeds, and glacial till deposits.
