Answer:
The most valuable thing in the world!
One day, Richard was walking home from school, it was about 12 blocks away, he was always a happy boy, singing and dancing on the street but this day was different, he wanted to cross the park to get home sooner. When he passed through the park, he found an envelope with a pendant inside, he picked it up and arrived home. Later, when he had lunch, he wanted to look at the pendant more carefully and he noticed that there was a picture of a girl, then, he continued looking inside the envelope and he found an address and the most amazing coincidence was that the address was his home, so he asked his mom if she knew the girl in the picture and she started crying and said, "Yes, it is my mom when she was 12, I think I would never recovered this pendant again because I lost it yesterday when I was crossing through the park". Finally, Richard knew that he did not find an object, he found the most valuable thing in the world for his mom.
The end!