Australia, Mexico, Ethiopia, and Brazil: four palettes of light
Opals are found in several parts of the world, but not all opals are equal. Each producing region gives the gem distinct characteristics, shaped by the specific geological conditions of each territory. Understanding these differences is essential for anyone who wants to know, collect, or work with opals with genuine expertise.
Australia: the historical market benchmark
Australia has been the world's largest opal producer for centuries, at certain periods accounting for approximately 95% of the global market. The main producing regions are Lightning Ridge (black opals), Coober Pedy (white and crystal opals), and White Cliffs.
The black opal of Lightning Ridge is considered the most valuable in the world: the dark background creates a contrast that dramatically intensifies the play of colors. Exceptional specimens reach values exceeding those of diamonds per carat.
Australian opals formed in Cretaceous sedimentary rocks, a geological context that shares similarities with the Piaui deposits, placing Brazil in excellent company.
Mexico: fire in the stone
Mexico is the origin of the celebrated fire opals, found primarily in the state of Queretaro. They are distinguished by a warm background of orange and red tones, which may or may not display an internal play of colors.
Unlike Australian and Piaui opals, Mexican opals have a volcanic origin, hosted in rhyolites and other igneous rocks. This difference in formation is reflected in their chemical characteristics and stability: Mexican opals can be more susceptible to crazing in environments with variable humidity.
Culturally, fire opals were already known and valued by pre-Columbian civilizations, especially the Aztecs and Mayans, who called them the stone of the bird of paradise.
Ethiopia: the new player that reshaped the market
From 2008 onward, the discovery of opal deposits in Ethiopia, first in the Wollo province and later in other regions, significantly altered the dynamics of the global market. Ethiopian opals, especially the so-called Welo opals, display exceptional play of colors and are available in considerable volumes, making them highly competitive in price.
A unique characteristic of Ethiopian opals is hydrophany: they absorb water and can temporarily alter their transparency and play of colors upon contact with liquids. This property can be interpreted as a flaw or a curiosity depending on context.
Brazil (Piaui): a distinct identity
The opals of Pedro II, in Piaui, occupy a singular place in this landscape. Formed in sedimentary sandstones of the Parnaiba Basin, they share a Cretaceous geological context with Australian opals but have developed their own aesthetic characteristics:
- High transparency: Piaui crystal opals are frequently compared to the finest in the world
- Variety of types: the region produces fire, crystal, white, and, more rarely, black opals
- Stability: lower tendency to crazing compared to Mexican opals
- Saturated colors: Piaui play of color tends toward vivid, highly saturated hues
Despite their internationally recognized potential, Brazilian opals have historically been undervalued relative to Australian ones, something that is gradually changing as gemologists and jewelers around the world come to know and acknowledge their quality.
Which to choose?
There is no single answer. Each origin produces a different aesthetic experience, and the choice should be guided by what the stone communicates, its individual quality, and its purpose within a piece of jewelry. What matters above all is knowing the provenance, understanding what you are acquiring, and, when possible, choosing the gem that carries the narrative most aligned with what you want to express.
Source: GOMES, C.B. et al. As Opalas do Piaui [The Opals of Piaui]. Brasilia: CETEM/MCTI, 2025. Part of Fortes Jewellery's educational gemology series, based on scientific research by the Centro de Tecnologia Mineral of Brazil's Ministry of Science, Technology and Innovation.