So far, possibly the coolest thing I have seen in Hawaii is the Green Sand Beach
. As far as I know, this is the only beach of its type in the world. The green comes from spheres of the gemstone peridot (crystals of the mineral olivine). It's literally a bejeweled beach. The gem is born of fiery lava, so you will find it associated with other igneous rocks. The shade of green depends on the amount of iron in the crystal matrix. This photo is of a handful of sand. As you can see, the green is very bright.