According to the audit, 516 "loaned astromaterials" were lost or stolen between 1970 and 2010. Probably a lot of them were ground up and snorted like drugs by teen astronauts in a misguided attempt to get high. At least one of them ended up in the hands of an 74-year-old lady in that sad moon rock caper we wrote about earlier this year.
So, that's a lot of astromaterials, sure, but NASA has 26,000 samples on loan, a space expert told Space.com, so 516 really isn't that much. The only solution to our national missing moon rock is to test every rock in America to make sure it's not secretly from the moon.