Is there a buildup of static electricity in a sandstorm?
Sandstorms occur in dry areas, particularly deserts. The sand particles are fairly uniform in size. As the dry sand moves due to the wind it begins a leaping process known as saltation. Quoting the Wikipedia article:


  the initial saltation of sand particles induces a static electric field by friction


The sand particles become polarized and as the particles begin to hit each other the polarization on each grain gets rearranged and the degree of polarization doubles with each interaction. With a build up of static electric charge lightning can develop.

The greatest build up of static charge occurs in sandstorms of intermediate thickness.