From space.com :
The news conference that will officially unveil what was discovered on Mars is scheduled for Monday, but NASA has already said that it wasn’t organic matter that was discovered.
http://www.space.com/18721-mars-rover-curiosity-discovery-monday.html
That's strange, my first thought was ice, not far from the camera, then I thought maybe Sprite Lightning:
http://en.m.wikipedia.org/wiki/Sprite_(lightning)
Me too, the last time I did a search the only thing that came up was the dust storm. Maybe they will wait for the 21st of December to make the announcement.