Sand composed almost exclusively of olivine grains is rare. Olivine is a common rock-forming mineral among certain igneous rocks but it is very unstable under the atmospheric conditions and will therefore decay quickly. The most famous example of a beach sand composed mainly of olivine crystals is Papakolea Beach near the southern tip of Hawaii Island (Big Island). Beach sands containing olivine are not rare in volcanic regions but sand samples containing as much olivine as Papakolea sand does are very hard to find. More about olivine-bearing sands is here: Is Papakolea the only green beach. Olivine is significantly denser than other common minerals. It allows waves to separate olivine from the rest and concentrate it on the beach.
Olivine sand from Hawaii Island. Olivine is green. White grains are biogenic in origin. One orange foram is on the left. The source of olivine there is a cinder cone that is constantly pounded by the seawaves. Some olivine grains are darker. This is a sign of weathering. They have been there for a longer time than the green freshmen. Width of the view is approximately 1 cm.
Vesicular (containing lots of former gas bubbles) olivine basalt from La Palma, Canary Islands. Such rocks are the source material of olivine in beach sands. Width of the view is approximately 10 cm.
It is also olivine basalt from La Palma although it contains no olivine anymore. These orange iddingsite (mixture of clay minerals and iron oxides) grains are all what is left of olivine. Black grains are augite crystals.
