Opal or Tourmaline
The name opal derives from the Greek Opallos, meaning "to see a change (of color)." Opals range in color from milky white to black with flashes of yellow, orange, green, red, and blue. An opal's beauty is the product of contrast between its color play and its background.
Tourmaline has become a favorite gemstone among jewelry designers and gem collectors the world over. Since it is available in a wide variety of colors, it is ideally suited to almost anyone's taste. Tourmaline also is known for displaying several colors in the same gemstone. One multi-color variety is known as watermelon tourmaline, and features green, pink, and white colors bands; to resemble its namesake, the gemstone is cut into thin slices having a pink center, white ring, and green edge. Tourmaline is found in many localities including Brazil, Afghanistan, East Africa, and the USA.
Source: American Gem Society