ALH84001 is the meteorite of the moment- one of the 6 Antarctic meteorites thought to have originated on the planet Mars, and the only one of these to contain abundant secondary minerals. These secondary minerals are almost entirely carbonates- in this picture, the orange bullseyes with black and white rims. Although these mineral grains aren't very large, no more than 200 microns across,the tantalizing clues they give concerning the Martian environment have lead some researchers to speculation of biogenic activity on that planet. However, other researchers, including the author, feel that interpretation is a bit premature given the enormous amount there is still left to learn about this meteorite.