Editing Flood basalt (section)

===Smaller-scale features===
Flood basalt commonly displays [[columnar jointing]], formed as the rock cooled and contracted after solidifying from the lava. The rock fractures into columns, typically with five to six sides, parallel to the direction of heat flow out of the rock. This is generally perpendicular to the upper and lower surfaces, but rainwater infiltrating the rock unevenly can produce "cold fingers" of distorted columns. Because heat flow out of the base of the flow is slower than from its upper surface, the columns are more regular and larger in the bottom third of the flow. The greater hydrostatic pressure, due to the weight of overlying rock, also contributes to making the lower columns larger. By analogy with Greek temple architecture, the more regular lower columns are described as the ''colonnade'' and the more irregular upper fractures as the ''entablature'' of the individual flow. Columns tend to be larger in thicker flows, with columns of the very thick Greenstone flow, mentioned earlier, being around {{convert|10|m|sigfig=1|sp=us}} thick.{{sfn|Philpotts|Ague|2009|p=55}}

Another common small-scale feature of flood basalts is ''pipe-stem vesicles''. Flood basalt lava cools quite slowly, so that dissolved gases in the lava have time to come out of solution as bubbles (vesicles) that float to the top of the flow. Most of the rest of the flow is massive and free of vesicles. However, the more rapidly cooling lava close to the base of the flow forms a thin [[chilled margin]] of glassy rock, and the more rapidly crystallized rock just above the glassy margin contains vesicles trapped as the rock was rapidly crystallizing. These have a distinctive appearance likened to a clay [[tobacco pipe]] stem, particularly as the vesicle is usually subsequently filled with [[calcite]] or other light-colored minerals that contrast with the surrounding dark basalt.{{sfn|Philpotts|Ague|2009|p=58}}