; ▁the ▁extensive ▁f ract ure ▁network ▁that ▁develop s ▁results ▁in ▁the ▁formation ▁of ▁columns . ▁The ▁topology ▁of ▁the ▁later al ▁shapes ▁of ▁these ▁columns ▁can ▁broad ly ▁be ▁class ed ▁as ▁a ▁random ▁cell ular ▁network . ▁These ▁structures ▁are ▁pre domin antly ▁hex ag onal ▁in ▁cross - section , ▁but ▁pol yg ons ▁with ▁three ▁to ▁twelve ▁or ▁more ▁sides ▁can ▁be ▁observed . ▁The ▁size ▁of ▁the ▁columns ▁depends ▁lo os ely ▁on ▁the ▁rate ▁of ▁cool ing ; ▁very ▁rapid ▁cool ing ▁may ▁result ▁in ▁very ▁small ▁( < 1   cm ▁diameter ) ▁columns , ▁while ▁slow ▁cool ing ▁is ▁more ▁likely ▁to ▁produce ▁large ▁columns . ▁ ▁Sub marine ▁er u ptions ▁ ▁P ill ow ▁bas al ts ▁▁ ▁When ▁bas alt ▁er u pts ▁under water ▁or ▁flows ▁into ▁the ▁sea , ▁contact ▁with ▁the ▁water ▁qu en ches ▁the ▁surface ▁and ▁the ▁la va ▁forms ▁a ▁distinct ive ▁pill ow ▁shape , ▁through ▁which ▁the ▁hot ▁la va ▁breaks ▁to ▁form ▁another ▁pill ow . ▁This ▁" p ill ow " ▁texture ▁is ▁very ▁common ▁in ▁under water ▁bas alt ic ▁flows ▁and ▁is ▁di agnostic ▁of ▁an ▁under water ▁er u ption ▁environment ▁when ▁found ▁in ▁ancient ▁rocks . ▁P ill ows ▁typically ▁consist ▁of ▁a ▁fine - gra ined ▁core ▁with ▁a ▁glass y ▁cr ust ▁and ▁have ▁radial ▁joint ing . ▁The ▁size ▁of ▁individual ▁pill ows ▁var ies ▁from ▁ 1 0   cm ▁up ▁to ▁several