The hydrated amorphous form of Silica is Opal. Silica is classified as a mineraloid due to its amorphous character. A mineraloid is a naturally occurring mineral-like substance that does not demonstrate crystallinity. This article will briefly throw light on Opal.

Opal – Common, Precious, Rare

• The two broad classes of opal are common and precious. Common opal does not display iridescence and precious opal displays iridescence.
• Opal may be opaque, translucent, and transparent.
• Green opal, grey opal, and white opal are the most common and black opal is the rarest.

Opal – Importance and History

• The national gemstone of Australia is Opal.
• Opal was rare and very valuable in antiquity.
• Opal was a gem prized by royalty in Europe.
• Until the 19th century, the only source of opal was Cervenica in Slovakia. Later on, vast deposits of Opal were discovered in Australia.

Opal – Sources Across the Globe

• The two main sources of opal across the globe are Australia and Ethiopia in Africa.
• As per some studies, Australia accounts for 95% to 97% of the world’s supply of precious opal.
• However, it is difficult to understand the accurate proportions of the global supply of opal due to varying and inconsistent accounts of extraction.

Opal Source – Australia

• In Australia, the region of South Australia accounts for 80% of the world’s supply of opal.
• In South Australia, the major source of opal is a town named Coober Pedy.
• A town named Lightning Ridge in New South Wales is the main source of black opal.
• A major producer of black opal, crystal opal, and matrix opal is Andamooka in South Australia.
• The Mintabie Opal Field in South Australia has produced large quantities of rarer black opal and crystal opal.
• “Olympic Australis” is the world’s largest and most valuable opal. This opal was found in August 1956 at the “Eight Mile” opal field in Coober Pedy.

Opal Source – Ethiopia

• The discovery of precious opal in the Menz Gishe District, North Shewa Province in Ethiopia in 1994 was the first published report of opal from Ethiopia.
• In 2008, a new opal deposit was found in the Wollo province of Ethiopia. The opal discovered in this province has been referred to as “Wello” or “Welo” opal. This opal has become the most dominant Ethiopian opal in the gem trade.

Related Links

• NCERT Notes: Geography – Some major minerals and their characteristics
• NCERT Notes: Geography – Physical characteristics of minerals
• NCERT Notes: Types of Rocks [Geography Notes for UPSC]