Nephrite Jade from Washington State, USA, Showing Optical Phenomena

Jandn-Pierre Jutras¹, Cara Williams², Bear Williams², George R. Rossman³

This article introduces a new nephrite jade type from Washington State (USA) that exhibits subtle to spectacular directional color variations in both daylight and artificial light, an optical phenomena not previously documented in the jade literature. Analytical studies performed on the material include EDXRF analysis, Raman spectrometry, thin section work and SEM/EDS characterization. These confirm that its mineralogical and gemological properties are consistent with that published for nephrite jades from other locations and indicate that the unique color-shift optical phenomenon are related to the underlying architecture of the tremolite fiber constituents of the jade. These show high angle to orthogonal cross-felting of numerous generations of fibres, often with varying underlying chemistry. The high translucency of the stone and relatively coarse tremolite fibres allows the pleochroism associated with monoclinic tremolite crystals to be revealed. In common jades, both the minute size and random orientation of constituent tremolite fibres diffuse light, and do not channel it. Cutting has shown that the stone has the toughness required to be cut into cabochons or carved without any treatment, passing the workability test as a true, yet new and unique jade type.