  The state of super-dense matter is essential for us to understand the nature
of pulsars, but the non- perturbative quantum chromodynamics (QCD) makes it
very difficult for direct calculations of the state of cold matter at realistic
baryon number densities inside compact stars. Nevertheless, from an
observational point of view, it is conjectured that pulsars could be made up of
quark clusters since the strong coupling between quarks might render quarks
grouped in clusters. We are trying an effort to find an equation of state of
condensed quark-cluster matter in a phenomenological way. Supposing that the
quark-clusters could be analogized to inert gases, we apply here the
corresponding-state approach to derive the equation of state of quark-cluster
matter, as was similarly demonstrated for nuclear and neutron-star matter in
1970s. According to the calculations presented, the quark-cluster stars, which
are composed of quark-cluster matter, could then have high maximum mass that is
consistent with observations and, in turn, further observations of pulsar mass
would also put constraints to the properties of quark-cluster matter. Moreover,
the melting heat during solid-liquid phase conversion and the related
astrophysical consequences are also briefly discussed.

Solar and Stellar Astrophysics;High Energy Physics - Phenomenology;Nuclear Theory