  Reformulation of Dirac equation in terms of real quadratic division algebra
of quaternions is given. Similar equations with different mass term are
identified as suitable for description of free propagating quark motion. The
complete orthonormal set of the positive-energy plane wave solutions is
presented. Therefore, Zitterbewegung phenomenon is absent in this formulation.
The probability current is proportional to the momentum, as in standard
Schrodinger wave mechanics.
