Igneous and metamorphicrocks are more compact, commonly crystalline, and rarely contain spaces between grains.
火成岩和变质岩比较致密，通常是结晶性的，颗粒之间很少有空隙。
2
Some very ancient sediments were no longer recognizable, having been converted to igneous and metamorphicrocks in the course of mountain building.
在造山的过程中，一些非常古老的沉积物已被转化为火成岩和变质岩，已经无法辨认了。
3
However, even igneous and metamorphicrocks may act as groundwater reservoirs if extensive fracturing occurs in such rocks and if the fracture system is interconnected.