Strange Matabei Crater on Mercury

When I was looking at the first color MESSENGER image of Mercury, I noticed a somewhat strange crater that seemed to have a "Fu Manchu" moustache of rays emanating from it. Fortunately, SPACE.com provided a labeled image of the first orbital shot from MESSENGER, that named the crater as Matabei (clicking image makes it bigger):
























Here's a closeup, with caption following. I'm sure that it will be interesting to see if the probe can figure out something about what the dark rays are made of.















"When a meteoroid strikes the surface of a planet, material from the target area is ejected outward at high velocity, often creating rays that extend over distances far greater than the size of the crater formed by the impact. During MESSENGER's second Mercury flyby, MDIS captured images of many impressive rays on Mercury, such as the ejecta prominent around Kuiper crater and the extensive ray system associated with the northerly Hokusai crater. For both of those examples, the rays appear bright, which is characteristic of freshly pulverized rock and indicates that the rays are younger than much of Mercury's surface. In contrast, in the center of this image, a set of dark rays can be seen emanating from the small crater Matabei. Dark rays are rare on Mercury, but other occurrences have been identified, such as at Mozart crater. Mozart is interpreted to have excavated dark material from depth during the impact event, creating dark streamers. The dark rays from Matabei may have a similar origin, and color images to be obtained during MESSENGER's orbital mission phase will be used to explore further the nature of these unusual dark rays."