Editing Flood basalt (section)

=== Petrology ===
At still smaller scales, the [[Texture (geology)|texture]] of flood basalts is [[aphanitic]], consisting of tiny interlocking crystals. These interlocking crystals give trap rock its tremendous toughness and durability.{{sfn|Philpotts|Ague|2009|p=55}} Crystals of [[plagioclase]] are embedded in or wrapped around crystals of [[pyroxene]] and are randomly oriented. This indicates rapid emplacement so that the lava is no longer flowing rapidly when it begins to crystallize.{{sfn|Philpotts|Ague|2009|p=53}} Flood basalts are almost devoid of large [[phenocrysts]], larger crystals present in the lava prior to its being erupted to the surface, which are often present in other extrusive igneous rocks. Phenocrysts are more abundant in the [[Dike (geology)|dikes]] that fed lava to the surface.{{sfn|Philpotts|Ague|2009|p=383}}

Flood basalts are most often [[quartz]] [[tholeiite]]s. [[Olivine]] tholeiite (the characteristic rock of [[mid-ocean ridges]]{{sfn|Philpotts|Ague|2009|p=366}}) occurs less commonly, and there are rare cases of [[alkali basalt]]s. Regardless of composition, the flows are very homogeneous and rarely contain [[xenoliths]], fragments of the surrounding rock ([[country rock (geology)|country rock]]) that have been entrained in the lava. Because the lavas are low in dissolved gases, [[pyroclastic rock]] is extremely rare. Except where the flows entered lakes and became [[pillow lava]], the flows are massive (featureless). Occasionally, flood basalts are associated with very small volumes of [[dacite]] or [[rhyolite]] (much more silica-rich volcanic rock), which forms late in the development of a large igneous province and marks a shift to more centralized volcanism.{{sfn|Philpotts|Ague|2009|p=381}}