Tetragonal crystal system
= Tetragonal crystal system
A <crystal system> with mutually perpendicular conventional cell axes and lengths $a=b\ne c$. The physical length of the direction $[uvw]$ is proportional to $\sqrt{a^2(u^2+v^2)+c^2w^2}$; crystallographic indices are coefficients in a lattice basis, not necessarily Cartesian components of equal scale.