 | Opal is a hydrated amorphous form of silica; its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. It is classified as a mineraloid, unlike the other crystalline forms of silica, which are classed as minerals.
The first published report of gem opal from Ethiopia appeared in the 1994, with the discovery of precious opal in the Menz Gishe District, North Shewa Province. The opal, found mostly in the form of nodules, is of volcanic origin and is found predominantly within weathered layers of rhyolite. In 2008, a new opal deposit was found near the town of Wegel Tena, in Ethiopia's Wollo Province. The Wollo Province opal was different from the previous Ethiopian opal finds in that it more closely resembled the sedimentary opals of Australia and Brazil, with a light background and often vivid play-of-color. Wollo Province opal, more commonly referred to as "Welo" or "Wello" opal became the dominant Ethiopian opal in the gem trade. |  |