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Opal

Oval-cut white opal weighing 14.59 ct.
Photo by Ken Larsen. Click to zoom.
SpecimenCatalog NumberLocalityWeight
OpalNMNH G10672-00Ethiopia14.59 ct
OpalNMNH G10673-00Ethiopia3.26 ct

Gift of Bill Marcue in 2011.

Opals from Mezezo, Ethiopia have been well-known since 2000 for their play-of-color chocolate opals. A more recent find of opal deposits was discovered in 2008 near Wegel Tena in the cliffs at Tsehay Mewcha in the province of Welo, Ethiopia. The opals from this area yield precious white, fire, crystal and sometimes black opals. The gems you see here are crystal opals weighing 14.59ct and 3.26ct and display a transparent body color exhibiting a brilliant play-of-color in red, orange, yellow, green, and blue. These opals also have interesting inclusions from what appear to be organic material, most likely from the roots of plants. The mining is done by local farmers with primitive tools and is extremely dangerous as they dig on the steep high ledges of the precarious cliffs that reach 3200m.

Gem opal consists of tiny silica spheres tightly packed together; the voids or spaces between the spheres contain air or water. The play-of-color in opal is due to the orderly arrangement of these spheres acting like a diffraction grating, breaking visible white light in to separate colors. Opals are typically cut en cabochon or polished free-form to best show this play-of-color.


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