mineraloid
Black Opal (Kalimaya)
Hydrated Silica (SiO2·nH2O)
Hardness: 5.5-6.5; Color: Black body color with multicolored pinfire play-of-color; Luster: Vitreous to waxy; Structure: Amorphous silica spheres; SG: 1.9-2.3
- Hardness
- 5
- Color
- Black body color with multicolored pinfire play-of-color
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 5.5-6.5; Color: Black body color with multicolored pinfire play-of-color; Luster: Vitreous to waxy; Structure: Amorphous silica spheres; SG: 1.9-2.3
Formation & geological history
Formed from silica-rich water seeping into cracks and cavities in volcanic or sedimentary rocks. The Indonesian variety (Kalimaya) is often associated with volcanic formations in Banten and surrounding regions.
Uses & applications
Primary use is for jewelry, particularly cabocahons, rings, and pendants, and as a highly sought-after collector gemstone.
Geological facts
In Indonesia, black opals are known as 'Kalimaya'. They are famous for their dark body tone which makes the 'fire' or play-of-color appear much more vivid than in white or crystal opals.
Field identification & locations
Identify by the characteristic 'play-of-color' (iridescence) against a dark background. Often found in Java (Banten region), matching the user's Indonesian coordinates. Check for internal flashes under light.
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