Chemistry:Golden sheen sapphire
| Gold/Golden Sheen Sapphire | |
|---|---|
 | |
| General | |
| Category | Oxide mineral |
| Formula (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 |
| |re|er}} | 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] |
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. doi:10.1063/1.357922. Bibcode: 1994JAP....76.8032H.
- ↑ 2.0 2.1 2.2 2.3 2.4 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". The Gem and Jewelry Institute of Thailand (Public Organization), Bangkok, 10500, Thailand July–August 2016: 282–288. http://www.git.or.th/2014/eng/testing_center_en/lab_notes_en/glab_en/2016/11/D5-A0210.pdf.
- ↑ "Update on spectroscopy of Gold Sheen Sapphire". The Quarterly journal of the gemological institute of america L11 (winter 2016): 413-414. https://www.gia.edu/doc/Gems-Gemology-Winter-2016v4.pdf.
- ↑ 6.0 6.1 "Gems&Jewellery Winter 2018 Volume 27 4 - The Gemmological Association of Great Britain". https://gem-a.com/component/edocman/gems-jewellery-winter-2018.
- ↑ 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/). 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.
- ↑ 10.0 10.1 10.2 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.
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