Where is Opal found?
Opal (amorphous hydrated silica)
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Open the appOpal occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Opal
Australia
The world's primary source of precious opal, particularly from localities like Coober Pedy, Lightning Ridge, White Cliffs, and Mintabie. Black opal from Lightning Ridge is particularly famous.
Ethiopia
A significant producer of Welo opal, known for its vibrant play-of-color and hydrophane properties (absorbs water and becomes more transparent).
Mexico
Known for fire opal (orange to red body color, sometimes with play-of-color) and water opal, often found in volcanic rocks.
Brazil
Produces common opal and some precious opal, often found in sedimentary formations.
United States
Localities in Nevada, Idaho, and Oregon produce various types of opal, including precious opal and common opal, often associated with volcanic activity.
Hungary (Slovakia)
Historically a major source of precious opal, particularly from the Dubník mines, though production is now limited.
Collecting tips
- Look for specific geological settings. Opal is often found in areas with ancient volcanic activity, sedimentary basins with silica-rich groundwater, or weathered zones of certain rock types. Look for areas with evidence of past hydrothermal activity or silica deposition.
- Examine host rocks. In Australia, opal is typically found in Cretaceous sedimentary rocks, often within ironstone concretions or sandstone layers. In volcanic settings, it can be found in vesicles or fractures in rhyolite or basalt.
- Check for 'potch' (common opal). Common opal often occurs alongside precious opal. Finding potch can be an indicator that precious opal might be nearby. Potch can be white, gray, black, or other colors, but lacks the play-of-color.
- Use a loupe or magnifying glass. Small flashes of color or subtle iridescence might be visible with magnification, especially when examining rough material.
- Wet the specimen. Some opals, particularly hydrophane opals, will show enhanced play-of-color or transparency when wet. This can help in identification, but be aware that some opals can crack if dried too quickly after being saturated.
- Safety Precautions. Opal itself is not hazardous. However, mining or collecting in certain geological environments may expose individuals to other hazards such as unstable ground, dust (which can contain crystalline silica), or other minerals. Always wear appropriate personal protective equipment (PPE) and be aware of your surroundings. When cutting or polishing opal, use wet methods to minimize dust inhalation, as fine silica dust can be a respiratory irritant.
Quick Check
- Color:
- Variable, often with 'play-of-color' in precious varieties.
- Luster:
- Vitreous to waxy.
- Streak:
- White.
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