These are so stunning if you like architectural antiques! 
I believe they are made from either a basalt stone or marble, though not entirely sure. I can tell you they are extremely heavy and your books would most definitely be held in place if that is what they are used for. 
They look equally beautiful placed on a coffee table or on top of a pile of books, stood on a shelf or simply propped up against the wall! Even use as door stops! 
Just stunning simplicity! 
** Priced individually 
Measurements: 12 x 9.5 x 33.5cm high