From Exsolution to 'Gold Sheen': A New Variety of Corundum.

De Corte, Katrien; Bui, Thanh Nhan; Deliousi, Katerina; Malik, Tanzim Khan

Sapphires displaying an attractive golden sheen reportedly were discovered in eastern Kenya in late 2009, and were recently brought to market in commercial quantities. The basic gemmological properties of the so-called Gold Sheen sapphires are consistent with typical corundum. Microscopic examination and Raman micro-spectroscopy showed that Fe-Ti oxides (hematite, ilmenite and magnetite) are the main solid inclusions, and they are oriented parallel to crystallographic directions in the basal pinacoid of corundum characterized by a six-fold rotational symmetry. Hematite and ilmenite are present in the form of exsolution intergrowths within platelets or needles. Magnetite typically appears as larger and thicker black platelets. The sheen effect in these sapphires originates from the simultaneous reflection of light from the oriented network of exsolved hematite-ilmenite inclusions.

SAPPHIRES; MICROSCOPY; CORUNDUM

Journal of Gemmology, 2015, Vol 34, Issue 8, p678

1355-4565

Academic Journal

10.15506/JoG.2015.34.8.678