Black Opal : What is it?
 Black opal is a mineraloid gel deposited at low temperatures in the fissures of almost any kind of rock. It is commonly found in sandstone, rhyolite, limonite, and basalt. Black opal has a black or gray base with a play of white, milky blue, gray, red, yellow, orange, brown, and green hues on the foreground. It usually has a water content of 3% to 10% that can be as high as 20%.
Black opal is very appealing to collectors. It is commonly used in jewelry as adornments. |
Kinds of Black Opals include the following:
Common black opal
- Common opal is truly amorphous.
- It is a gemstone variety that features a play of colors.
Precious black opal
- Precious opal is amorphous.
- It shows a variable interplay of internal colors.
- It is composed of cubic or hexagonal, closely-packed, silica spheres around 150 to 300 nm in diameter.
- The silica spheres produce the internal play of colors by causing the interference and diffraction of light that passes through the black opal.
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Colors: Choose a black opal with a lively play of colors when light is reflected on it.
Base: To highlight the different colors on the foreground, choose a black opal with a very dark base.
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