Gemmological and Spectral Characteristic of Sapphire from Australia

Australia is a major producer of sapphire. The main purpose of this study is to analyze the gemmological and spectrcal characteristics of sapphire samples from Australia, and to provide a theoretical basis for the treatment of sapphires. The gemmological and spectral characteristics of sapphire samples from Australia were studied by using the conventional gem test, Fourier transform infrared spectroscopy (FTIR), laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS), micro-ultraviolet-visible spectroscopy (UV-Vis) and laser Raman spectroscopy. The result showed that the specific gravity of sapphire samples from Australia is 3.74-4.20, N_e=1.762-1.770, N_o=1.770-1.778, DR=0.008, and strong glass gloss and inertia under ultraviolet fluorescent lamp. Blue and yellow hexagonal colour zone, healing fissures and inclusions are extremely common in sapphire sample from Australia, where have kinds of solid inclusions, two-phase inclusions and healing fissures. Infrared peaks such as 630, 519, 490, 454, 436 cm^-1 in the fingerprint region, and absorption peak at 3 310 cm^-1 indicated that these sapphires from Australia grew in reducing condition.The chemical composition and geological origin by LA-ICP-MS, showed that the Cr/Ga ratio is less than 1 and the Fe/Ti ratio is mostly between 10-100, which is the ratio of typical magmatic sapphire, and the iron content is between 3 230×10^-6-9 431×10^-6. Comprehensive analysis of UV-Vis absorption spectroscopy and chemical compositions turns out that the colour is mainly relevant to the content of Fe, Ti, Si, Mg. Absorption peaks of 377, 387 and 450 nm are caused by the d-d electronic transition of Fe³⁺ and Fe³⁺—Fe³⁺ in the region with less Ti; Fe²⁺—Ti⁴⁺charge transfer leads to the yellow green region absorption band centered at 559 nm in the region with multiple Ti; Fe²⁺—Fe³⁺ charge transfer often occurs with Fe²⁺—Ti⁴⁺ charge transfer, and causes the wide absorption band in 700-800 nm centered in 754 nm, center may shift with different ratio of the charge transfer of Fe²⁺—Fe³⁺ and Fe²⁺—Ti⁴⁺. Raman spectroscopy showed that the inclusions mainly include two-phase inclusion (CO₂ and H₂O), sapphire, rutile, zircon, diaspore, amphibole and so on, sulphur on healing fissures means that S element participated in the transaction of sapphire.