My dumortierite is mainly dark, with one side that is covered in lighter speckles. I'm not certain how the shades of blue affect the energy,though..
My herkimer diamond is around 2 - 2.5cm long.I'm not sure if I should even call it a Herkimer diamond, considering one end is damaged ; but I'm almost certain that there was indeed a double termination. It also has a tiny little rainbow in it.