Liberia 25 Dollars 2020 0.5g Gold with opal Observe Coat of Arms of Liberia divides date Reverse Maori designs, opal insert. Composition Gold (.9999) (With peel off opal Weight 0.5 g Diameter 11 mm Shape Round Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt. With CoA