igneous
Gabbro (Stream-rounded Pebble)
Gabbro (Phaneritic Mafic Igneous Rock)
Hardness: 6-7 (Mohs scale), Color: Dark grey to greenish-black with light specks, Luster: Dull to sub-vitreous, Crystal Structure: Phaneritic (visible crystals), Specific Gravity: 2.7-3.3
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale), Color: Dark grey to greenish-black with light specks, Luster: Dull to sub-vitreous, Crystal Structure: Phaneritic (visible crystals), Specific Gravity: 2.7-3.3
Formation & geological history
Formed through slow crystallization of magnesium-rich and iron-rich magma beneath the Earth's surface (intrusive). This specimen was later eroded and tumbled by river or stream action.
Uses & applications
Crushed stone for road construction, railroad ballast, and dimension stone known as 'Black Granite' in the decorative stone industry.
Geological facts
Gabbro is the intrusive equivalent of basalt and makes up a significant portion of the deep oceanic crust.
Field identification & locations
Identify by its dark color, coarse grain size, and weight compared to lighter rocks. Commonly found in mountainous regions or riverbeds downstream from igneous outcrops.
