Green opal - Natural minerals and crystals

Opal is a mineraloid, meaning it does not have a perfectly ordered crystal structure like most minerals. It is primarily composed of hydrated silica, which is silicon dioxide combined with water. Depending on the size and arrangement of these spheres, opal can exhibit a wide range of colors, from milky white to deep black and all shades of the rainbow. It is this characteristic that makes opal a highly prized gemstone in jewelry. Opal formation is related to complex geological processes. It is usually formed in sedimentary environments, by precipitation of silica from aqueous solutions. The main opal deposits are found in Australia, Mexico, Brazil and the United States. Opals are often associated with silica-rich volcanic or sedimentary raw rocks and minerals">rocks. The quality and value of an opal depends on several factors, such as clarity, colour, play of light and size.