Quarks are elementary particles and fundamental constituents of matter.  They have various intrinsic properties, including electric charge, mass, colour charge and spin.

They are the only elementary particles in the Standard Model of Particle Physics to experience all four fundamental interactions, known as fundamental forces (i.e. electromagnetism, gravitation, strong interaction and weak interaction), as well as the only known particles whose electric charges are not integer multiples of the elementary charge.

There are six “flavours” of quarks:

up, down, strange, charm, top, bottom.

Up and down quarks have the lowest masses of all quarks.  The heavier quarks rapidly change into up and down quarks through a process of particle decay: the transformation from a higher mass state to a lower mass state.

For that reason, up and down quarks are generally stable and the most common quarks in the Universe, whereas the strange, charm, bottom, and top quarks may only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators).

For every flavour of quark, there is a corresponding type of anti-particle – an antiquark, that differs from the quark in that some of its properties have equal magnitude but opposite sign.