1. The problem statement, all variables and given/known data In a mock exam I was asked for Q. Two properties associated with a single crystal. 2. Relevant equations 3. The attempt at a solution For one answer I gave that they are hard. I think another answer might have been something to do with crystal planes as this is what the teacher said when going over the paper again. I was wondering what this might be? Are crystal planes the same thing as grain boundaries? Thanks very much.