The Halley's Comet Opal is the largest uncut black

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline form ...

in the world, according to the Guinness Book of World Records. It is so named because it was unearthed in 1986, a year when

Halley's Comet Halley's Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–79 years. Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and thus the on ...

could be seen from Earth. It is the third largest gem grade black opal ever recorded, the largest one extant, and the largest specimen ever found in its region. It was found at

Lightning Ridge, New South Wales Lightning Ridge is a small outback town in north-western New South Wales, Australia. Part of Walgett Shire, Lightning Ridge is situated near the southern border of Queensland, about east of the Castlereagh Highway. The Lightning Ridge area is ...

, Australia by the Lunatic Hill Mining Syndicate. It weighs (13.99 ounces) and is about the size of a man's fist. The Halley's Comet Opal is a very fine specimen, with few flaws or blemishes and a large green and orange thick color bar which goes through the opal. Formed about 20 million years ago, it is an example of a nobby, which is a natural lump-shaped opal found only at Lightning Ridge. As of 2006 it was for sale at $1.2 million.

References

Individual opals {{Mineral-stub

See also

References