One of the most intriguing phenomena in strongly correlated systems is
the fractionalization of quantum numbers - familiar examples include 
the spin-charge separation in one-dimensional metallic systems, 
the fractionalization of the electron in certain quantum Hall states 
or the emergence of monopoles in spin ice.

In this talk, I will discuss the fractionalization of magnetic 
moments in a certain class of Mott insulators, in which the emergent 
degrees of freedom are Majorana fermions that form an (almost) 
conventional metal. The origin of such a dichotomous state is 
elucidated by a family of exactly solvable models of frustrated 
quantum magnets in three dimensions, which might be realized in 
a class of recently synthesized Iridate compounds. These models 
thereby provide the first analytical tractable examples of long 
sought-after quantum spin liquids with a spinon Fermi surface and 
even an entire new class of quantum spin liquids - a so-called Weyl 
spin liquid, in which the fractionalized degrees of freedom form 
a topological semi-metal.