Short version for those not inclined to read a whole story on Mars and the growing evidence that it was once a warmer, wetter planet. Rover found a softball sized grey hematite rock. Hematite can be formed by volcanic activity, but grey hematite more commonly forms in places that once had standing water or hot springs. The real test will be to see whether the hematite is filling cracks in rocks (which would indicate it traveled by water) or embedded in ash (indicating it was formed by a volcanic process).
http://www.space.com/scienceastronomy/mars_hematite_040203.html The black hole article
http://www.space.com/scienceastronomy/heavy_blazar_040628.html