▁links ▁ ▁Wait omo ▁District ▁Council ▁ ▁Category : Pop ulated ▁places ▁in ▁Wa ik ato ▁Category : Wait omo ▁District <0x0A> </s> ▁Bas alt ▁( , ▁) ▁is ▁a ▁ma fic ▁extr us ive ▁ igne ous ▁rock ▁formed ▁from ▁the ▁rapid ▁cool ing ▁of ▁mag nes ium - rich ▁and ▁iron - rich ▁la va ▁exposed ▁at ▁or ▁very ▁near ▁the ▁surface ▁of ▁a ▁terrest rial ▁planet ▁or ▁a ▁moon . ▁More ▁than ▁ 9 0 % ▁of ▁all ▁vol can ic ▁rock ▁on ▁Earth ▁is ▁bas alt . ▁Bas alt ▁la va ▁has ▁a ▁low ▁vis cos ity , ▁due ▁to ▁its ▁low ▁sil ica ▁content , ▁resulting ▁in ▁rapid ▁la va ▁flows ▁that ▁can ▁spread ▁over ▁great ▁areas ▁before ▁cool ing ▁and ▁solid ification . ▁Flo od ▁bas alt ▁describes ▁the ▁formation ▁in ▁a ▁series ▁of ▁la va ▁bas alt ▁flows . ▁ ▁Definition ▁▁ ▁By ▁definition , ▁bas alt ▁is ▁an ▁a phan it ic ▁( f ine - gra ined ) ▁ igne ous ▁rock ▁with ▁generally ▁ 4 5 – 5 3 % ▁sil ica ▁( Si O 2 ) ▁and ▁less ▁than ▁ 1 0 % ▁f eld sp ath oid ▁by ▁volume , ▁and ▁where ▁at ▁least ▁ 6 5 % ▁of ▁the ▁rock ▁is ▁f eld s par ▁in ▁the ▁form ▁of ▁pl agi oc l ase . ▁This ▁is ▁as ▁per ▁definition ▁of ▁the ▁International ▁Union ▁of ▁Ge ological ▁Sciences ▁( I U GS ) ▁classification ▁scheme . ▁It ▁is ▁the ▁most