This article is about the elementary particle and its antiparticle. For other uses, see Quark (disambiguation).QuarkA proton is composed of two up quarks, one down quark, and the gluons that mediate the forces "binding" them together. The color assignment of individual quarks is arbitrary, but all three colors must be present; red, blue and green are used as an analogy to the primary colors that together produce a white color.Composition elementary particleStatistics fermionicGeneration 1st, 2nd, 3rdInteractions strong, weak, electromagnetic, gravitationSymbol qAntiparticle antiquark (q)Theorized Murray Gell-Mann (1964)George Zweig (1964)Discovered SLAC (c. 1968)Types 6 (up, down, strange, charm, bottom, and top)Electric charge +2/3 e, −1/3 eColor charge yesSpin 1/2 ħBaryon number 1/3A quark (/kwɔːrk, kwɑːrk/) is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.[1] All commonly observable matter is composed of up quarks, down quarks and electrons. Owing to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons (such as protons and neutrons) and mesons, or in quark–gluon plasmas.[2][3][nb 1] For this reason, much of what is known about quarks has been drawn from observations of hadrons.