Igneous and metamorphic rocks 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
However, even igneous and metamorphic rocks may act as groundwater reservoirs if extensive fracturing occurs in such rocks and if the fracture system is interconnected.
然而，如果火成岩和变质岩中发生大规模的断裂，并且断裂系统相互连通，那么它们也可以作为地下水储集层。
3
Some very ancient sediments were no longer recognizable, having been converted to igneous and metamorphic rocks in the course of mountain building.