Is an amorphous solid a single phase? Amorphous solid possess short-range order but no long-range order (e.g. amorphous silica, the short-range order is originated from the tetrahedral bonding between Si and O). Is it possible to have multiple domains with different short-range orders in one amorphous solid? 

If so, should we treat this solid as a single phase or multiple phases? Can we detect the existence of multiple domains?

Relative concept: polyamorphism

(It seems that polyamorphism implies that amorphous phases can be distinct from each other.)



Amorphous silica, https://en.wikipedia.org/wiki/Structure_of_liquids_and_glasses
It is difficult to give a general answer. A glass is an amorphous solid that may change its composition in a continuous way from one point to another. When melting brown bottles and colorless bottles in the oven of a glass factory, you may obtain a non homogeneous mixture, with regions more or less colored. It is obviously one and the same phase all over the mixture. But as the mixture is not homogeneous, its composition is not the same everywhere.