Polished sphere of Orbicular Jasper so named on account of the characteristic rounded forms (orbicules) often seen in this rock. It is also known as Ocean Jasper . It is a mainly siliceous (SiO2) rock, comparable to agate or chalcedony, that was precipitated in a rhyolitic volcanic environment. Provenance is from a renowned location in Northern Madagascar. Actual diameter of sphere is 220 mm.