I read this book one summer back in the 70's at my grandparents house in S.E. Kansas. Found it in the public library... so glad I did. The storyline probably changed the course of my life. Largely because as a young kid the book was about young kids; it was about science ("old" and "new"); about a band of kids who learned the truth of an interesting alien invasion of "crystals" which could build things, and their attempts to save them from the adults who wanted to wipe them out. Once Amazon came around and I could actually find a used copy on-line and could buy it - I did. If you're looking for a great story - this is one!