I have heard that Granite is the best for inground concrete pools, if it is constantly submerged, as it is hardly or not at all porous, which keeps it from collecting debris or cultivating the growth of algae, also does not hold water like a sponge that other more porous rocks may do. Sandstone I've heard is ok for waterfall type rocks, not sure on that though.
No. Stone is natural. We mine certain types of rock for natural resources.
There are three main types of inground swimming pools: concrete, vinyl and fiberglass. All of which are prone to the occasional crack. Luckily for the homeowner such cracks can be repaired. If you are handy you can purchase a do it yourself repair kit at your local pool specialty store.
I am aware of none. After the introduction of gunpowder, castles became obsolete very quickly. However, they were replaced by forts made of natural stone, artificial stone, compacted earth, wood, or a combination of these.
Cast stone, also known as a refined architectural concrete building unit is manufactured to simulate natural cut stone. These stones are used in unit masonry applications./