Gabbro
Image: Wilson44691 (Mark A. Wilson at the Wayback Machine, Department of Geology, The College of Wooster). (Public domain)
Mineral NameGabbro
Chemical FormulaComplex silicate (rock composed primarily of plagioclase and pyroxene)
Mohs Hardness6
Streak ColorGray to greenish-gray
CleavageNot applicable (rock); constituent minerals exhibit cleavage (e.g., plagioclase: 2 directions at ~90°, pyroxene: 2 directions at ~90°)
FractureUneven to subconchoidal
Specific Gravity2.8
Colorsdark gray, black, greenish-black
TransparencyOpaque
Type LocalityRock Creek Canyon, eastern Sierra Nevada, California
Mineral GroupIgneous rock (mafic, intrusive)
Usesconstruction aggregate, dimension stone, countertops, road material
Associated Mineralsplagioclase feldspar, pyroxene, olivine, amphibole, magnetite, ilmenite
Raritycommon
Description
A dark gray to black, coarse-grained igneous rock specimen with visible interlocking crystals, exhibiting a somewhat rough, uneven surface and a few brighter, reflective mineral grains.
Geological Context
Gabbro is a mafic intrusive igneous rock that forms from the slow crystallization of magnesium- and iron-rich magma deep beneath the Earth's surface. It is the intrusive equivalent of basalt and is a major component of the lower oceanic crust.
