Mosaic map
The pictures in the article sure looked like mud puddles at first, but not when taking in the whole panarama. Of course, my pet hypotheisis is that there are vast oil reserves on Mars. So naturally, the dark, slick-looking spots looked like sludge oil oozing out of the crazily-crossbedded-or-otherwise-jumbled-up whitish top formation. However, if you magnify toward the right, you can see similar spots where the rover left tracks. Also, to the very far left in the distance, there seem to be similar spots on the ridges there, yet the white, top formation is missing, therefore the white, top formation is probably not the source of the material comprising the slick-looking spots.
I agree that it's probably
hematite or those magnetic, iron "filings" from meteors we used to collect with magnets when we were kids. Essentially, the crater rim is a naturally formed, aeolian gold pan. The slick spots are aeolian deposits of very dense, very fine dust particles.
If you're a panner on Earth, cracks like those found in the exposed bedrock of the crater lip are the best places to look for gold in the bedrock beneith a stream. So it's quite likely that that the slick-looking spots are rich in gold dust as well.