Basalt is a hard, black volcanic rock with less than about
52 weight percent silica (SiO2). Because of basalt's low
silica content, it has a low viscosity (resistance to flow).
Therefore, basaltic lava can flow quickly and easily move
>20 kilometers from a vent. The low viscosity typically
allows volcanic gases to escape without generating
enormous eruption columns. Basaltic lava fountains and
fissure eruptions, however, still form explosive fountains
hundreds of meters tall. Common minerals in basalt include
olivine, pyroxene, and plagioclase. Basalt is erupted at
temperatures between 1100 to 1250° C.
(USGS/VHP)

Svart bergart dannet ved størkning av flytende
lavamasserunder vulkanske utbrudd.

Basalt er en av de mest utbredte bergarter på jorden,
og danner mye av berggrunnen under verdenshavene
og store lavaplatåer på land.