How a crystal grows and is shaped influences its vibration - that which we feel is its energy assistance. So this too is important in how we respond to a crystal and its healing help for us not just its colour, internal structure and mineral content.
The shape - external or something "within" it - means our eyes are receiving visual cues that may trigger a happy or sad memory which we can then work with. The shaping by man also influences whether we feel a crystal helps. A crystal shaped as an Angel may help you to feel supported.