Basalt
Image: <a href="//commons.wikimedia.org/wiki/User:Chmee2" title="User:Chmee2">Chmee2</a> (CC BY 3.0)
Mineral NameBasalt
Chemical FormulaComplex, primarily silicates of Fe, Mg, Ca, Na, K, Al
Mohs Hardness5
Streak ColorWhite to grayish-white
CleavageNot applicable to rock; constituent minerals (e.g., pyroxene, plagioclase) have good cleavage
FractureConchoidal to uneven
Specific Gravity2.9
Colorsdark gray, black, brownish-black
TransparencyOpaque
Type LocalityGiant's Causeway, Northern Ireland
Mineral GroupIgneous rock (extrusive volcanic rock)
Usesconstruction material, aggregate, paving stones, dimension stone, rock wool insulation
Associated Mineralsplagioclase feldspar, pyroxene (augite), olivine, magnetite, ilmenite
Raritycommon
Description
The image displays a dramatic coastal landscape featuring dark, hexagonal columnar basalt formations, with ocean waves crashing against the shore under a partly cloudy sky.
Geological Context
Basalt is an extrusive igneous rock formed from the rapid cooling of mafic lava flows on the Earth's surface or underwater. The distinctive columnar jointing, as seen at the Giant's Causeway, develops as thick lava flows cool and contract.
