Golden sheen sapphire
(repeating unit)Aluminium oxide, Al2O3 Crystal system Trigonal Crystal class Hexagonal scalenohedral (3m)
H-M symbol: (32/m) Space group R3c Identification Color Typically metallic gold, copper or bronze, blue, green but varies Crystal habit As crystals, massive and granular Fracture Conchoidal, splintery Mohs scale hardness 9.0 Luster Vitreous Specific gravity 3.95–4.03 Optical properties Abbe number 72.2 Refractive index nω=1.768–1.772
nε=1.760–1.763,
Birefringence 0.008 Pleochroism Strong Melting point 2,030–2,050 °C Fusibility Infusible Solubility Insoluble Other characteristics Coefficient of thermal expansion (5.0–6.6)×10−6/K
relative permittivity at 20 °C
ε = 8.9–11.1 (anisotropic).[1]
H-M symbol: (32/m)
nε=1.760–1.763,
Birefringence 0.008
relative permittivity at 20 °C
ε = 8.9–11.1 (anisotropic).[1]
Golden sheen sapphire, (or goldsheen sapphire) is a recently discovered variety of corundum.[2] Goldsheen sapphire has been tested and confirmed in lab reports as "natural sapphire" by GIA, GIT, GRS, AIGS, Tokio gem labs and Lotus.
Goldsheen sapphire has a golden shine, almost like gold. Translucent blue, green or yellow material is sometimes present together with the gold.[3][2] Particularly prominent is hematite which will often result in the formation of geometric hexagonal patterns within the gemstone crystal.[4]
Evidence
Several articles, including the Journal of Gemmology state that gold sheen sapphire is high in iron and titanium oxide.[2] It has inclusions of ilmenite, hematite (gold color)[5] and magnetite (black). It exhibits asterism and hexagonal growth,[6] a lack of UV fluorescence, healed fractures and polysynthetic twinning (parallel lines). Golden sheen has a stronger golden shine and sometimes has blue and gold in the same stone.[2]
Source
Previously, it was claimed in the Journal of Gemmology (JoG),[2] that the source is a depleted mine in Kenya close to the border of Somalia. TJN Colors, GIT and In Color [7][8][9] also previously published that the origin was Kenya. However, GIA Tokyo [10] and Gems and Jewellery [6] stated in 2018 that the location is not known. GIA [10] and JoG stated that golden sheen sapphires are reportedly mined in northeastern Kenya, there is no other published chemical data available from this region[10]
References
- ^ 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.
- ^ a b c d e 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".
- ^ Journal of Gemmology. volume 35 no.5 https://gem-a.com/component/k2/volume/volume-35-no-5-2017-2-2 Pages 430-435
- ^ 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.
- ^ "Update on spectroscopy of Gold Sheen Sapphire" (PDF). The Quarterly journal of the gemological institute of america. L11 (winter 2016): 413–414.
- ^ a b "Gems&Jewellery Winter 2018 Volume 27 4 - The Gemmological Association of Great Britain". gem-a.com. Retrieved 2023-10-19.
- ^ 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.
- ^ Unninayar, Cynthia; "Gold Sheen Sapphires – From Gold Mine to Market" (2018) (https://gemstone.org/incolor/38/92/ Archived 2018-06-14 at the Wayback Machine). In Color: Summer 2018, Pages 92-95.
- ^ "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.
- ^ a b c 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.
