The last two people on the moon were Eugene Cernan and Harrison Schmitt, who were about of the Apollo 17 mission in 1972. While they were on the moon, they decided to take back a brick-sized piece of moon rock. They wanted to share it with different countries around the world. All they had to do was break it apart when they returned to earth.
Schmitt brought the moon rock back to Earth. It was given to President Richard Nixon, who had it broken up and mounted on plaques. Each plaque had the flag of the country it was going to be gifted to, and just a small piece of moon rock. One such piece was given to Ireland, 1 of 135 pieces of moon rock that were distributed.
The moon rock in Ireland was put in the Dunsink Observatory. Interest in the Apollo missions waned, and people began to pay very little attention to what happened to that little rock. In 1977, the Observatory burned down. The remains of the Observatory were put in the nearby dump, and no one thought to sort the moon rock out of the other debris. The rock was buried in the dump, and has not been found.
More recently, people have been interested in finding the rock again. Financial troubles in Ireland, make that little, expensive rock very appealing. Many people have tried to dig through the dump, in hopes of finding that tiny treasure among the trash.