[Pa pa (Golden Plover) ko le a (flats)]. I took advantage of a day for myself this week and went out for a walk exploring the Big Island of Hawaii.
Green sand beaches are very rare and there are only a few in the world. One is in Central Siberian Yupik another is on Floreana Island the Galapagos, one on Guam and the one with the highest concentration of mineral and the greenest of the green sand beaches is at Papakolea near South Point.
The terrain at South Point (Ka Lae) 0n the Big Island of Hawaii is a plateau of elevated windy, dry grassland and pasture. There are only a handful of homes in the lower portion of the south point, mostly for horseman and cattlemen. There is a boat launch for local fisherman and a coastal trail that leads to Mahana Bay and Green Sands Beach – (18 deg 56’10.40″N, 155 deg 38’46.00W)
More than 49,000 years ago a volcanic cinder cone (Pu’u Mahana) formed several miles up the easterly side of the coast. The cone is rich in olivine, a silicate material containing iron and magnesium. Olivine is a common mineral in Hawaiian lava and is one of the first minerals to form as the magma cools. The small green mineral specks in the rocks pictured are called a phenocryst. This rock is an example of the porphyrtic basalt found around Papakolea. Porphyritic rocks are formed when a column of rising magma starts cooling slowly beneath the crust and then a second more rapid cooling of the magma occurs from an erupting volcano or while at near the surface, creating small mineral crystals in the process. In this case phenocryst olivine basalt. The larger crystal olivine that is of gem quality is called Peridot. (didn’t find any.)
Mahana Bay has formed inside the collapsed cinder cone Pu’ u Mahana. The cone is made of layers of ash and cinder built over numerous eruptions. As erosion wears away the remaining walls of the crater, olivine is exposed and collects at the base forming a narrow band of green beach. Lighter weight ash and grey sand is washed away by the sea leaving the denser olivine crystals. The constantly eroding headland replenishes the beach with a lasting supply of cascading green sand.
I discovered this other pocket of green sand gems at Papakolea near Ka Lae in Ka’u on my walkabout. Have you found any gems lately? Get out doors, walk for your health and explore the beauty of the Earth.