Where is Blue Opal in Host Rock found?
Opal (SiO2·nH2O) in host rock
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Open the appBlue Opal in Host Rock 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 Blue Opal in Host Rock
Oregon, USA
Known for blue opal found in volcanic host rocks, particularly rhyolite. Examples include the Opal Butte area.
Nevada, USA
Various localities yield common blue opal in volcanic and sedimentary host rocks.
Indonesia
Some regions produce blue common opal, often associated with volcanic activity and petrified wood.
Peru
Known for its distinctive blue opal, often found in nodular or massive forms within host rock.
Australia
While famous for precious opal, common blue opal also occurs in various sedimentary and weathered environments.
Collecting tips
- Look for Volcanic or Sedimentary Environments. Focus on areas with past volcanic activity (rhyolite, basalt flows) or sedimentary basins with evidence of silica-rich water circulation, such as hot spring deposits or weathered zones.
- Identify Host Rock Characteristics. Familiarize yourself with the common host rocks for opal in a given region. Look for fractures, vugs, or altered zones within these rocks that might contain opal.
- Observe Luster and Fracture. Opal's characteristic waxy to vitreous luster and conchoidal fracture can help distinguish it from surrounding host rock minerals. Look for these features in exposed surfaces.
- Check for Translucency. Common blue opal is often translucent to opaque. Hold specimens up to light to check for light transmission, which can help differentiate it from opaque host rock.
- Consider Hardness. Opal is relatively soft (5.5-6.5 on Mohs scale). While not a definitive test in the field, it can help distinguish it from harder quartz or chalcedony in some cases.
Quick Check
- Color:
- Blue (various shades) within a contrasting host rock
- Luster:
- Vitreous to waxy or resinous (for opal)
- Streak:
- White
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