Usually I prefer not to speculate on this sort of thing, because if we just wait we'll have a ton more information soon. However, I wonder if it could be a fulgerite: http://en.wikipedia.org/wiki/Fulgurite
Interesting theory. I had to check, and yes, Mars does have dry lightning (in dust storms). If not that, I wonder if it's something produced volcanically like onyx.
Either that or a door handle! :P