  Two kinds of difficulties have challenged the physics community for many
years: (1) knowing nature's building blocks (particle physics) and (2)
understanding interacting many-body systems (many-body physics). Both of them
exist in the research of quark matter and compact stars. This paper addresses
the possibility that quark clustering, rather than a color super-conducting
state, could occur in cold quark matter at realistic baryon densities of
compact stars, since a weakly coupling treatment of the interaction between
quarks might not be reliable. Cold quark matter is conjectured to be in a solid
state if thermal kinematic energy is much lower than the interaction energy of
quark clusters. Different manifestations of pulsar-like compact stars are
discussed, as well as modeled in a regime of solid quark stars.
