Gemmological and Spectroscopic Characteristics of Multi-coloured Crystal from Canada

The multi-coloured crystal from Thunder Bay, Canada, commercially known as "Auralite 23 Crystal", is a rare crystal variety first discovered in Thunder Bay area along the northern shore of Lake Superior in Ontario, Canada. To date, there have been few international studies on this type of multi-coloured crystal, and no relevant domestic literature on Canadian amethyst has been reported. In this study, microscopic imaging, infrared spectroscopy and Raman spectroscopy techniques were employed to systematically analyze the gemmological characteristics, inclusion morphology and mineral components, along with comparative research on its origin, in order to provide theoretical support for further investigation of Canadian multi-coloured crystals. The overall colour of the multi-coloured crystal samples from Canada exhibited purple, dark brown, to deep red tones, and polished samples showed a refractive index of 1.545- 1.553, with the relative density ranging from 2.64-2.65, and no fluorescence was detected under long-wave or short-wave ultraviolet radiation, consistent with the characteristics of α-quartz group minerals.Rough stones typically occur as crystal clusters, with triangular growth hills visible on the crystal terminations. Inclusions are mainly concentrated in white and dark purple zones, displaying diverse morphological features such as sheet-like, block-like, cluster-like, and short acicular forms. In some areas, multiple inclusions are mixed, with lengths ranging from 10-1 000 μm and widths from 1-10 μm. Infrared spectroscopy revealed characteristic absorption peaks at 400-600 cm^-1, 700-800 cm^-1, and 1 100-1 200 cm^-1. Raman spectroscopy indicated that black and red inclusions are hematite, golden cluster-like inclusions are goethite, metallic cubic block inclusions are pyrite, and the red surface layer consists of densely aggregated concentric-ring hematite inclusions within the near-surface crystal.