Golden sheen sapphire

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Gold/Golden Sheen Sapphire
Blue sheen and gold sheen sapphire.jpg
General
CategoryOxide mineral
Formula
(repeating unit)
Aluminium oxide, Al2O3
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (32/m)
Space groupR3c
Identification
ColorTypically metallic gold, copper or bronze, but varies
Crystal habitAs crystals, massive and granular
FractureConchoidal, splintery
Mohs scale hardness9.0
LusterVitreous
Specific gravity3.95–4.03
Optical propertiesAbbe number 72.2
Refractive indexnω=1.768–1.772
nε=1.760–1.763,
Birefringence 0.008
PleochroismStrong
Melting point2,030–2,050 °C
FusibilityInfusible
SolubilityInsoluble
Other characteristicsCoefficient of thermal expansion (5.0–6.6)×10−6/K
relative permittivity at 20 °C
ε = 8.9–11.1 (anisotropic).[1]

Golden Sheen Sapphire, is a name that is known to be associated with golden sapphire. It typically shows a metallic golden colour with translucent material also possible. It has the same color, chemical properties[2][3] and features as black star sapphire.

Particularly prominent is hematite which will often result in the formation of geometric hexagonal patterns within the gemstone crystal.[4]

The term 'gold sheen' or 'gold sheen effect' was first described by the GIA testing laboratory in Bangkok in 2013. Samples of the gemstone were tested to confirm they were true sapphire and the colour was described as 'brown, with gold sheen effect'.

Questions regarding evidence and claims[edit]

Two articles from the Journal of Gemmology state that both black star and gold sheen are high in iron and titanium oxide, which accounts for the brown/black color. They have inclusions of ilmenite, hematite (gold color) and magnetite (black). Both exhibit asterism and hexagonal growth, a lack of UV fluorescence, healed fractures and polysynthetic twinning (parallel lines). Although declared as a "new variety"[5], there remains the question of its extremely close similarity to black star sapphire, [6] [7] which comes from more than ten countries in the world. [8][9]


Gemological labs that have issued certificates categorizing golden sheen sapphire as corundum, describing the gold sheen effect as 'known in the industry as gold sheen sapphire', include: GIA, GRS, LOTUS, GIT, SSEF, AIGS, IGL.

Source[edit]

GIA Tokyo [10] and Gems and Jewellery [11] admitted in 2018 that the location is not known. GIA [12] and JoG [13] mention that there is no evidence of gemstone deposits in the flat border region near Somalia.

Previously, it was claimed in the Journal of Gemmology (JoG)[14], that the source is a depleted mine in Kenya close to the border of Somalia. TJN Colors, GIT and In Color [15][16][17] also previously published that the origin was Kenya.


Optical effects[edit]

Color change[edit]

Golden Sheen Sapphire will exhibit mild to strong color change under warm, cool and direct sunlight.[citation needed]

Gold sheen sapphire color change example using warm (3000k), cool (5000k) and natural sunlight

Asterism[edit]

All cabochon cut Golden Sheen Sapphire will exhibit some degree of asterism.[citation needed]

Tray of gold sheen sapphire cabochons displaying asterism

Heating and treatment[edit]

There are no known heating or treatment methods for golden sheen sapphire.[citation needed] Testing of heat treatment on sample batches has resulted in diminishment of the gold sheen effect, reducing the appeal of the gemstone.[citation needed]

Use in jewellery[edit]

Golden sheen sapphire has been used in jewelry production by companies including

Awards[edit]

In 2016 a gold sheen sapphire ring by William Travis Jewelry won the American Gem Trade Association Savor Silver Award, Men's Wear.[18]

References[edit]

  1. ^ Harman, Alang Kasim; Ninomiya, Susumu; Adachi, Sadao (1994). "Optical constants of sapphire (alpha-Al2O3) single crystals". Journal of Applied Physics. 76 (12): 8032–8036. Bibcode:1994JAP....76.8032H. doi:10.1063/1.357922.
  2. ^ Journal of Gemmology. volume 35 no.5 https://gem-a.com/component/k2/volume/volume-35-no-5-2017-2-2 Pages 430-435
  3. ^ Journal of Gemmology. volume 34 no.8: pages 678–691. Bui T.N., T.N.; Deliousi, K.; Malik T.K., T.K.; De Corte, K. (2015). "From exsolution to 'gold sheen': A new variety of corundum".
  4. ^ Nalin Narudeesombat, Saengthip Saengbuangamlam, Thanapong Lhuaamporn and Thanong Leelawatanasuk (2016). "Golden Sheen and Non-Sheen Sapphires from Kenya" (PDF). The Gem and Jewelry Institute of Thailand (Public Organization), Bangkok, 10500, Thailand. July–August 2016: 282–288.
  5. ^ Bui T.N., T.N.; Deliousi, K.; Malik T.K., T.K.; De Corte, K. (2015). "From exsolution to 'gold sheen': A new variety of corundum". Journal of Gemmology. 34 (8): 678–691.
  6. ^ Bui T.N.; Entremont, Pascal; Gauthier. Jean-Pierre; (2017) "Large 12-Rayed Black Star Sapphire from Sri Lanka with asterism caused by Ilmenite Inclusions" (https://gem-a.com/component/k2/volume/volume-35-no-5-2017-2-2). Journal of Gemmology. volume 35 no.5 Pages 430-435.
  7. ^ Bui T.N., T.N.; Deliousi, K.; Malik T.K., T.K.; De Corte, K. (2015). "From exsolution to 'gold sheen': A new variety of corundum" (https://gem-a.com/education/resources/application-and-downloads/syllabus/3250- from-exsolution-to-gold-sheen-a-new-variety-of-corundum-journal-of-gemmology-34-8-678-691/). Journal of Gemmology. 34 (8): 678–691.
  8. ^ AJS Gems, "Black Star Sapphire Gemstone Information" (2019) (https://www.ajsgem.com/gemstone-information/black-star-sapphire-27.html)
  9. ^ Hughes, Richard, "Moontown: A history of Chanthaburi, Thailand and Pailin, Cambodia" (2011) (http://www.ruby-sapphire.com/chanthaburi-history-of-moontown.htm)
  10. ^ Katsurada, Y; Miura M.; Saruwatari, K. "Golden Sheen Sapphire and Syenite/Monzonite–Hosted Sapphire From Kenya" GIA Tokyo: Gems & Gemology, Fall 2018, Pages 322-323.
  11. ^ Bui T.N. "Shimmering Sapphires" (https://gem-a.com/news-publications/gems-jewellery) Gems and Jewellery: Winter 2018, P36-39.
  12. ^ Katsurada, Y; Miura M.; Saruwatari, K. "Update on trace-element chemical characteristics of golden sheen sapphire." (https://www.gia.edu/gems-gemology/summer-2018-gemnews-update-on-trace-element-chemical-characteristics-of-golden-sheen-sapphire) Spring 2018, Vol. 54, No. 2.
  13. ^ Bui T.N., T.N.; Deliousi, K.; Malik T.K., T.K.; De Corte, K. (2015). "From exsolution to 'gold sheen': A new variety of corundum". Journal of Gemmology. 34 (8): 678–691.
  14. ^ Bui T.N., T.N.; Deliousi, K.; Malik T.K., T.K.; De Corte, K. (2015). "From exsolution to 'gold sheen': A new variety of corundum". Journal of Gemmology. 34 (8): 678–691.
  15. ^ Wheat, Barbara; “Aesthetic to the core” (2016) (http://www.tnjcolors.com/Issues/V3_I2/V3_I2.html). TJN Colors volume 3, issue 2. Pages 60-61.
  16. ^ Unninayar, Cynthia; "Gold Sheen Sapphires – From Gold Mine to Market" (2018) (https://gemstone.org/incolor/38/92/). In Color: Summer 2018, Pages 92-95.
  17. ^ "Golden Sheen and Non-Sheen Sapphires from Kenya" (https://www.git.or.th/eng/testing_center_en /lab_notes_en/glab_en/2016/11/D5-A0210-1.pdf)(PDF). The Gem and Jewelry Institute of Thailand.
  18. ^ "2016 AGTA Spectrum Awards Winners". www.agta.org. Archived from the original on 2016-11-17. Retrieved 2016-12-06.