Puu Mahana Beach (Green Sand beach) is the spectacular erosion product of a volcanic cinder cone near South Point on the Big Island of Hawaii. It can be reached by a 1-hour hike through beautiful scenics (take plenty of water!). The unusual tone of the green sand is due to the large proportion of semi-precious stone olivine polished crystals, which are left behind during the breakdown of lava. Crystals of olivine form in abundance during the cooling of hot lava. Because they are much harder than the lava matrix, they tend to accumulate near areas of lava erosion.