I suggest reading [ame=http://www.amazon.com/Man-Moon-Andrew-Chaikin/dp/0140272011]Amazon.com: A Man on the Moon (9780140272017): Andrew Chaikin, Tom Hanks: Books[/ame].
It talks quite a bit about the moon rocks and how astronauts/scientists came about finding out that the craters were really from meteorite impacts, but they kept trying to find evidence that there were volcanoes on the moon. The book illustrates why this is important. The author has interviewed many astronauts as well as other big players of the Apollo program so he made a "story" out of the collected personal accounts. It's really an interesting book.