Except at extreme temperatures and pressures, atoms form the three classical states of matter: solid, liquid and gas.
At high temperatures or strong electromagnetic fields, atoms become ionized, forming plasma.
Magnetic states such as ferromagnetism and antiferromagnetism can also be regarded as phases of matter in which the electronic and nuclear spins organize into different patterns.
Metallic and insulating states of materials can be considered as different quantum phases of matter connected by a metal-insulator transition.
Materials can be classified by the structure of their Fermi surface and zero-temperature dc conductivity as follows:[4]