De que estan hechas las rocas
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Las rocas están constituidas, en general, por mezclas heterogéneas de diversos materiales homogéneos y cristalinos, es decir, minerales. ... Las rocas suelen ser materiales duros, pero también pueden ser blandas, como ocurre en el caso de las rocas arcillosas o las arenosas.

Explanation:

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

hope this