 Chiral symmetry breaking is most apparent in the mass generation of nucleons from more elementary light quarks, accounting for approximately 99% of their combined mass as a baryon.It thus accounts for most of the mass of all visible matter.For example, in the proton, of mass "mp" ≈ 938 MeV, the valence quarks, two up quarks with "mu" ≈ 2.3 MeV and one down quark with "md" ≈ 4.8 MeV, only contribute about 9.4 MeV to the proton's mass.