Why aren't these rocks RED?
The red colour of Mars comes from the oxidization of iron minerals due to weathering. The less weathered rocks appear grey or black. This also indicates that Mars must have had a different atmospherethan it does today.
How did they get here?
About 16 million years ago Mars was bombarded by meteorites and/or an asteroid which must have reached a velocity of 5.4 km/s and would have left a crater of 10-100 km in diameter. This ejected pieces of the crust into space, which would have floated around for several million years until they came into earth's atmosphere about13 000 years ago.
What do they tell us?
There must have been a differentation of the mantle, core and crust of Mars about 4.5 billion years ago (similar to Earth). Many of the samples show evidence of interaction with water, as seen in alteration products such as salt and clay caused by weathering. They also tell us that the evolutionof the Martion atmosphere was different to that of Earths, in that the gasses that were needed to support life escaped early in the history of the planet.
Some of the meteorites that have been determind as comming from mars.