  The chiral nonanalytic behaviour of quark-flavor contributions to the
magnetic moments of octet baryons are determined in full, quenched and
partially-quenched QCD, using an intuitive and efficient diagrammatic
formulation of quenched and partially-quenched chiral perturbation theory. The
technique provides a separation of quark-sector magnetic-moment contributions
into direct sea-quark loop, valence-quark, indirect sea-quark loop and quenched
valence contributions, the latter being the conventional view of the quenched
approximation. Both meson and baryon mass violations of SU(3)-flavor symmetry
are accounted for. Following a comprehensive examination of the individual
quark-sector contributions to octet baryon magnetic moments, numerous
opportunities to observe and test the underlying structure of baryons and the
nature of chiral nonanalytic behavior in QCD and its quenched variants are
discussed. In particular, the valence u-quark contribution to the proton
magnetic moment provides the optimal opportunity to directly view nonanalytic
behavior associated with the meson cloud of full QCD and the quenched meson
cloud of quenched QCD. The u quark in Sigma^+ provides the best opportunity to
display the artifacts of the quenched approximation.
