|All solid opals can be placed on a scale of lightness and darkness of their body tone. Darker body tone opals are called black opals. Lighter body tone opals are light opals. The darker the opal for the same quality and colour range, the pricier it is.
Opals with a high level of transparency are also referred to as crystal opals, which can be either black (black crystal opals) or light (light crystal opals).
Boulder opals may also be either black or light, depending on their body tone. Invariably, they form in brown ironstone host rock, with which they are usually cut. Because of the geologically unique environment that produces them, they have become to constitute an opal type to themselves.
Pipe opals are very rare, especially those of brilliant Jundah quality. They take shape of a “pipe” of a different thickness and colour, often with a level of transparency that creates hypnotic multidimensionality.
Opal doublets and opal triplets are composite stones. They are made to offer the aesthetics of solid opals at a fraction of their price. Opal doublets have two layers. A slice of natural opal is glued to a background of darker, often boulder, slice. Opal triplet has three layers. A very thin slice of opal is glued on black background and covered with a see-through dome of resin or quartz, which gives it a characteristic glassy appearance.
Due to its limited availability, best quality solid opals are pricier per carat than other gemstones.
Unlike some other gemstones, opals are never mined on a grand scale, nor can they be controlled by the interests of large companies. Opal miners often work alone. Each of them is a unique and picturesque character. Just like the gemstones that lured them into a harsh lifestyle, each is one of a kind.