igneous
Gabbro or coarse-grained dioritic rock
Plutonic mafic/intermediate rock; typically plagioclase feldspar + pyroxene ± amphibole/biotite
AI-generated identification · may be incorrectDark gray, speckled, granular, and weakly lustrous with interlocking crystals; Mohs hardness about 6–7, no obvious cleavage as a whole, and specific gravity roughly 2.7–3.1. The small rounded specimen appears weathered or tumbled, so exact identification from the photo is uncertain.
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Physical properties
Dark gray, speckled, granular, and weakly lustrous with interlocking crystals; Mohs hardness about 6–7, no obvious cleavage as a whole, and specific gravity roughly 2.7–3.1. The small rounded specimen appears weathered or tumbled, so exact identification from the photo is uncertain.
Formation & geological history
Formed when magma cooled slowly deep within Earth, allowing visible crystals to grow; commonly Precambrian to Cenozoic, depending on its intrusion. A definitive name requires mineral proportions or testing.
Uses & applications
Used as crushed stone, road aggregate, riprap, and occasionally dimension stone; attractive polished pieces are collected but rarely used as gemstones.
Geological facts
Gabbro is the coarse-grained intrusive equivalent of basalt, while diorite is its lighter, intermediate counterpart. The visible pale and dark interlocking grains suggest feldspar with mafic minerals.
Field identification & locations
Look for a hard, dense, salt-and-pepper texture and interlocking grains; a streak test is usually white to gray, and a knife will not easily scratch it. Common in oceanic crust and continental intrusive complexes worldwide.
