The NASA News item A Piece of Mars is Going Home begins:
A piece of a meteorite called Sayh al Uhaymir 008 (SaU008) will be carried on board NASA's Mars 2020 rover mission, now being built at the agency's Jet Propulsion Laboratory in Pasadena, California. This chunk will serve as target practice for a high-precision laser on the rover's arm.
which is pretty cool. But what caught my attention is:
NASA's Mars Global Surveyor included a chunk of a meteorite known as Zagami. It's still floating around the Red Planet onboard the now-defunct orbiter.
From the Wikipedia article I found the paper Zagami, Enriched Basaltic Shergottite, 18 kg but so far can't find which piece went (almost) back to Mars.