What are the two main characteristics for ALL igneous rocks?

Igneous rocks form from the cooling and solidification of lava or magma.

I'm not a big fan of this question, but I think the "desired" answer is grain-size (from very large to microcrystalline) and interlocking texture.

(It could be tendentiously argued that tuff (also called tufa) and possibly other pyroclastic rocks, which form from volcanic ejecta, lack an interlocking texture because they are more like sediments that are welded together. I say this is tendentious because such rocks are about as much sedimentary as they are igneous, and are not typical igneous rocks if they are igneous rocks at all.)