These rocks cool in a short time, for they are exposed to the air and give off heat and harden rather quickly. The mineral grains that form during this fast cooling do not have much time and chance to grow.

• 由于熔岩喷出地表接触空气，热散发快，岩石冷却结晶的时问短，岩石中矿物晶体没有足够的时间和机会生长。