I remember almost nothing about this book except the cover and the fact that I loved it. The cover was blue, with a picture of a glass mountain on it, and a couple of little witches on broomsticks flying around it. I read it in the early 1970’s when I took it out of the library and it was probably aimed at 10 – 12 year olds. I realize this is not a lot to go on! But thank you for any help anyone can offer.