大部分结晶岩石都非常坚硬，但也有例外，最常见的就是玄武岩，它是一种火山岩浆凝固后的形态，内部充满了微小的气泡，因此也具有多孔渗水的特点。
Most crystalline rocks are much more solid; a common exception is basalt, a form of solidified volcanic lava, which is sometimes full of tiny bubbles that make it very porous.
坚硬的火山岩是一种多年来需求量很大的资源，至少从奥尔梅克人（一种生活在公元前1200年至400年之间的民族）崛起以来是这样。
The hard volcanic stone was a resource that had been in great demand for many years, at least since the rise of the Olmecs (a people who flourished between 1200 and 400 B.
罗马人观察到，当火山灰与水混合然后冷却，火山灰变得非常坚硬，几乎不可能分解。
The Romans observed that, when volcanic ash mixes with water and then cools, it gets extremely hard and almost impossible to break up.
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