|Dimensions (mm)||18 x 12 x 10mm|
|Weight (carats)||41.2 carats|
"WELO" FIELD OPAL ETHIOPIA
This natural untreated stone parcel that is from the Welo area of Ethiopia.I purchased this material from a miner in Addis Ababba. He told me that he had been mining with not much luck when he hit this firey opal with his pick and he said he nearly cried. I think i would too as this parcel has top neon fire.I left the whole parcel on the bench for over 9 months before i decided to polish it to make sure it was sound opal after its rough birth in to the world. I decided to leave the stones as natural as possible as when they were found. I did thsi by placing the parcle in a tumbler and changing the grit to get a nice finish.You can still see where the pick shattered some areas of the stones.. This is a out standing collectors piece or it would suit a creative jeweler
It is showing multi neon colours of GREEN ORANGE RED.
Transulant with silky caramel base tone.
Body tone N-5
Brightness scale [B1 brightest] B1
Weight smallest to largest
41.20 cts app
THIS IS A WELL POLISHED HIGH DOME STONE SO YOU WILL SEE THE REFLECTION FROM THE LIGHTS
Opal Body Tone Scale as per recommendation by the Opal Association.
FROM OPAL ACCOCIATION
[BI BRIGHTEST TO B7 DULLEST]
This is what the GIA has to say about this type of opal
A new source of high-quality play-of-color opal was discovered in early 2008 in Welo Province, Ethiopia, about 500 km north of Addis Ababa. This deposit is geographically distinct from the Mezezo deposit in Shewa Province, which was discovered in the early 1990s (see, e.g., Spring 1994 Gem News, pp. 52–53).
These contributors examined a parcel of about five rough and 30 cut Welo opals. The cabochons showed good play-of-color ; the vast majority were white and transparent, but some had a bodycolor varying from light yellow to dark “chocolate” brown. Compared to Mezezo opals (e.g., J.-P. Gauthier et al., “L’opale d’Ethiopie: Gemmologie ordinaire et caractéristiques exceptionnelles,” Revue de Gemmologie a.f.g., No. 149, 2004, pp. 15–23), those from the new deposit generally appear much whiter. We noted all spectral colors in the play-of-color in our samples. Most of the cabochons were similar in appearance to opals from Australia or Brazil. However, many samples displayed a columnar structure of play-of-color opal within common opal (figure 2), as first described in material from Mezezo (again, see Gauthier et al., 2004). This feature is only very rarely observed in opals from sources outside Ethiopia.
The hydrostatic SG of the opals ranged from 1.80 to 2.10. This broad range is in part due to the high porosity of some samples, as revealed by a significant weight increase after immersion in water (up to 8%). Fluorescence varied from inert to moderate yellowish white to both long- and short-wave ultraviolet (UV) radiation. Samples that were inert displayed an unexpected greenish phosphorescence of moderate intensity. No luminescence was observed in the opals with a yellow-to-brown bodycolor, even the light ones; these darker bodycolors are probably due to the presence of iron, which quenches luminescence. The yellow-to-green luminescence is likely due to the presence of uranium (E. Gaillou et al., “The geochemistry of gem opals as evidence of their origin,” Ore Geology Reviews, Vol. 34, 2008, pp. 113–126). Fourier-transform Raman spectra were obtained for several samples using a Bruker RFS 100 spectrometer. All spectra were consistent with opal-CT, with Raman bands at about 1070, 780, 670, and 345 cm-1, and water-related bands at about 3200 and 2950 cm-1.
Welo opal is found in volcanic rock, possibly a rhyolite. The rough samples we examined consisted of opal (either common or play-of-color) cementing fragments of the host rock. By contrast, opal from Mezezo fills cavities in rhyolite, forming nodules. Despite these differences, the fact that columnar structures are seen in opals from both deposits (but very rarely from elsewhere) seems to indicate similarities in the conditions of their formation.
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|Starts||29th Oct 2019 4:02pm PDT|
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