Why solids aren't organized in simple cubic (SC) and Simple Hexagonal(SH) ?

[ShizukaSm]

My book mentioned that SC and SH are both "Theoretical arrangement" for crystal lattices, and later posed the question "Why it doesn't happen?", however it never provided an answer.

Well, I can 'sort of' (very non-scientifically, mind you) imagine why, three stacked layers of spheres(atoms) would rather fall in an alternate pattern than stay in perfectly tangential organization, Is there a better answer however? I mean, a better reason?

Thanks in advance

 

[toastisme]

My guess is, firstly SC (1 atom per unit cell) is rare in nature as BCC (2 atoms per unit cell) and FCC (4 atoms per unit cell) are more efficient forms of cubic packing and so are more common. I'm not sure about SH.
Secondly, it doesn't happen in nature because nothing is a perfect crystal of pure material. There's always impurities, dislocations, vacancies etc.

 

[DrDu]

I think simple cubic is realized in a high pressure allotroph of phosphorus and is the most stable structure at normal pressure and temperature of polonium. So it is quite exotic but possible.

 

[chill_factor]

isn't cesium chloride SC?

 

[DrDu]

isn't cesium chloride SC?

There are plenty of examples with a simple cubic or hexagonal lattice, but I suppose what the OP meant was crystal structures with a simple cubic or hexagonal lattice and a one-atom basis.