When working with nature, as in gardening, ritual or elementals, use crystals in their natural forms. When using gems and crystals for yourself, tune in to the shape that feels right for you. Man-made shapes actually harmonize beautifully with the human body. So much of the construction and function of our bodies is circular, cyclic or in various geometric configurations.
Be fairly literal when choosing the right crystal shape for the job. Especially for physical health. Choose heart shaped stones to strengthen the heart, little crystal sphere for the eyeballs, egg shapes for glands, slabs for teeth, crystal pyramid for kidneys, and wands for long bones. Ammonite fossils are helpful where you need spiral energy, such as blood circulations, curly hair, umbilical cord, etc.
Serpentine is a great stone for your skin for recovery after surgery, but you may want to also include another palm stone that is close in tone to your flesh tone.