I have found this list of densities here: http://wiki.chemprime.chemeddl.org/index.php/Density_of_Black_Holes
and I am looking for the density of quarks but I have not found it. I was wondering if Black Holes could be some kind of quark plasma (QGP). Is this possible?
The "Density of a black hole" is misleading. A black hole is a VACUUM solution to the Einstein's equations.
If you are interested in the biggest possible density of matter, then look at neutron stars. These are solutions to the full Einstein's equations with matter.
The composition of the core of neutron stars is still an open problem. In some models you can find exotic matter, even heavy baryons and quark-gluon plasma. Is estimated that the central density can range between $10^{14}- 10^{15} \rm g/cm^3$.
Some References:
-Neutron Star Observations: Prognosis for Equation of State Constraints (2006) (See p. 9)
