Natural opal is a semi-precious stone that is formed by the deposition of hydrated silica in the cracks and voids of volcanic rocks. Exposed natural opal has an oval caboson shape, i.e., it is worked into a domed shape without facets. The colour of this natural opal is white to yellow, its size is 10.20x8.20x5.80 mm, and its weight is 2.40 carats. The clarity of this opal is very good, with no inclusions visible to the naked eye and faint iridescence with little play of colour, predominantly red. The opal is untreated, i.e., it has not undergone any chemical or thermal process to improve its appearance or durability. The origin of natural opal is Ethiopia, one of the most important sources of opals in the world.