Glass on Mars

At http://news.discovery.com/space/mars-dark-spots-120402.html … a piece on the discovery of glass on the surface of Mars – and explanations offered. Dark patches visible across much of the northern hemisphere of Mars are not canals or other geological features as once thought, in the dimmer past, but volcanic glass – via data from ESAs Mars Express Orbiter. It is unclear if this is glass as we might understand it or something else. It is also described as basalt – and basalt has an origin in magma from volcanic and seismic activity. A comparison is made with Iceland, which is interesting, as when a volcano explodes beneath a glacier it can create sand sized black particles – and the Mars feature is dark. These Icelandic examples also form dunes like sand dunes, hence I imagine the conjecture towards glass, and they cover large parts of the Icelandic landscape. As the Mars glass is also dark and there are similar dune systems a similar origin might be in order – but why describe it as glass?