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 gemstone variety of the mineral corundum, an aluminium oxide (α-Al2O3). It typically shows a metallic golden colour with common variations being brass, copper and bronze, however metallic blue, green and yellow colouration is also possible. A very rare variation is a metallic red colour.

Unlike normal sapphire, golden sheen sapphire occurs principally as a result of iron and titanium inclusions, making the gem mostly opaque. In this respect, golden sheen sapphire is more like opal than other typically clear or transparent gemstone. Identified inclusions in golden sheen sapphire are ilmenite, rutile, hematite and magnetite. Particularly prominent is hematite which will often result in the formation of geometric hexagonal patterns within the gemstone crystal.[2]

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'.

Recognition as a variety of corundum[edit]

The Gemmological Association of Great Britain published an in-depth analysis of golden sheen sapphire in the Journal of Gemmology.[3]

The Gemological Institute of Thailand published their own independent analysis.[4]

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 and discovery[edit]

Golden sheen sapphire is only known to come from one source, an undisclosed mine in the north east of Kenya near the Somali border. Gem-A note “To our knowledge, no corrundum deposits have been reported in areas near Somalia.” (Page 689, Journal of Gemmology)[5]

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]

Other names[edit]

The name 'golden sheen sapphire' is often shortened to 'gold sheen sapphire' and the name is interchangeable.

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.[6]

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. ^ 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.
  3. ^ 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.
  4. ^ "Golden Sheen and Non-Sheen Sapphires from Kenya" (PDF). The Gem and Jewelry Institute of Thailand.
  5. ^ Thanh Nhan Bui, Katerina Deliousi, Tanzim Khan Malik and Katrien De Corte (2015). "From Exsolution to 'Gold Sheen': A New Variety of Corundum". The Journal of Gemmology. 34 (8): 678–691.
  6. ^ "2016 AGTA Spectrum Awards Winners". www.agta.org. Archived from the original on 2016-11-17. Retrieved 2016-12-06.