Are all planes in minerals crystal faces?
Yes, there are other planes. Most crystal have fracture planes which are not the same as the faces (some crystals have conchoidal fracture surfaces, curving surfaces which are not planes because they are not flat). SOme fracture planes are close to perfect and can trick you into thinking you are looking at a face. Many crystals have twinning planes, a plane from which a new crystal of the same material starts to grow.
