• Location: Andamooka, Australia
• Weight: 2.1g = 10.8ct
• Dimensions: 2.2 x 1.6 x 0.3 cm
• DETAILED DESCRIPTION

Australian opal is renowned worldwide as the most important source of high-quality opals. The quality of Australian opals is primarily due to their intense and pure play-of-color. Thanks to specific formation conditions, they often display vibrant and highly contrasting hues. This diversity is reflected in the many varieties of opals offered by Australia: from black and boulder opals to crystal, white, and matrix opals. Australian opals are notably more durable and stable than many opals from other locations. Their lower natural water content increases their resistance to variations in temperature and humidity, reducing the risk of cracks or drying out and making them ideal for everyday use in jewelry. Formation Australian opals generally form in sedimentary rocks such as sandstone and clay found in vast basins, for example the Great Artesian Basin, an enormous underground water system that extends over much of the Australian interior. Siliceous water gradually penetrates small fissures or pores in the rock. When this water evaporates or drains away, thin layers of silica remain in the cavities and can slowly transform into opal. Microscopic spheres of silicon dioxide (silica) play a fundamental role: they arrange themselves in a regular three-dimensional structure similar to a crystal. This configuration creates the characteristic "play-of-color," the iridescent effect visible in opal when light hits it. The color and intensity of this effect depend on the size and arrangement of these spheres. Deposits Andamooka is a small mining town in South Australia located approximately 600 kilometers north of Adelaide. It lies near the salt lake Lake Torrens, in a landscape characterized by an arid climate and difficult conditions. However, rich opal veins were discovered here in the 1930s, making Andamooka one of Australia's oldest opal mining fields. History Although Andamooka is not as famous as Coober Pedy or Lightning Ridge, opal mining here has a long tradition. Many mines are still family-run and use manual labor or small machinery. In the past, Andamooka, like other Australian mining fields, attracted adventurers seeking precious opal veins and the chance to make a fortune in extreme conditions. Types of Australian Opal Black Opal – the rarest and most precious variety, famous above all for the Lightning Ridge deposit in New South Wales. It features a dark base (black, grey, or dark blue) that enhances the play-of-color. Black opals often show the most intense color spectrum, including red, green, blue, and purple. Boulder Opal – primarily mined in Queensland. It forms when opal fills thin veins in iron-rich sandstones or other host rocks. This variety often retains part of the original rock, creating a contrasting base. Boulder Opals can have darker tones and therefore display a vivid play-of-color similar to that of black opals. Crystal Opal – characterized by a transparent or translucent base. In its rough state, it can appear almost colorless, but the iridescence becomes evident through a crystalline or milky base. Crystal Opals are found throughout Australia, with larger quantities coming from Coober Pedy. White Opal (Light Opal) – this variety has a white or milky white base. It can display colors as brilliant as those of black opals, but the light background tends to soften the visual contrast, making the effect less intense. White opals are particularly common in Coober Pedy and generally more accessible than black or boulder opals. Matrix Opal – a particular variety where opal is embedded in a porous rock, such as sandstone or ironstone. After impregnation treatments, the colors can become much more intense as the dark substrate accentuates the opal's play-of-color. Andamooka is especially famous for these matrix opals, called Andamooka Matrix, which after treatment can resemble the rare black opals from other locations. Value Andamooka opals are prized primarily for their relatively affordable prices and rich color patterns. However, high-quality specimens can reach high values, especially those that display an intense play-of-color or particularly spectacular patterns, such as the harlequin pattern.