igneous
Likely gabbro or dark amphibolite
Gabbro: coarse-grained mafic rock composed mainly of plagioclase and pyroxene; possible amphibolite: hornblende and plagioclase
AI-generated identification · may be incorrectDark gray, massive, weathered, and granular with weakly visible interlocking crystals; typically Mohs 5–6, vitreous to dull luster, no obvious cleavage as a whole, and specific gravity about 2.8–3.2.
Identified More igneous →
Explore Likely gabbro or dark amphibolite in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, massive, weathered, and granular with weakly visible interlocking crystals; typically Mohs 5–6, vitreous to dull luster, no obvious cleavage as a whole, and specific gravity about 2.8–3.2.
Formation & geological history
Gabbro crystallizes slowly from mafic magma deep in oceanic or continental crust, commonly Precambrian to modern; amphibolite forms when basalt or gabbro is metamorphosed under medium- to high-grade conditions.
Uses & applications
Used as crushed stone, aggregate, road base, riprap, and occasionally dimension stone; generally low jewelry value unless polished as a decorative specimen.
Geological facts
Its dark color reflects abundant iron- and magnesium-rich minerals. A magnet may show weak attraction if magnetite is present, but this image alone cannot reliably distinguish gabbro from amphibolite.
Field identification & locations
Common in oceanic crust, layered mafic intrusions, and metamorphic belts worldwide; identify with a hand lens by dark interlocking grains and pale plagioclase, then confirm using hardness, streak, magnetism, and thin-section analysis.
