Ancient Script-Like Serpentine in Brown Peridot
Peridot is a green olivine often characterized by “lily pad” inclusions and high birefringence causing a doubling effect. Apart from its familiar green hue, peridot can also possess a brown color, though these gems receive little attention.
Recently, the author found a xenocryst of peridot from southeast Vietnam that appeared black in daylight and brown through a transmitted light source. Standard gemological testing of a cabochon (2.51 ct) and two faceted stones (2.35 and 4.65 ct) that were cut from this xenocryst indicated peridot, but the specific gravity and refractive index gave higher results than the values for green peridot. Finally, the Raman spectra confirmed the identification as peridot.
Microscopic examination did not reveal any typical “lily pad” inclusions. Instead, there were innumerable fascinating thread-like inclusions (see above). Some formed closed loops with round, oval, and distorted shapes measuring from a few nanometers to a millimeter. Others stretched or twisted together like tangled threads up to 2 mm long. The display was reminiscent of an ancient script. Micro-Raman spectral analysis revealed these thread-like inclusions were serpentine.
Examination of this brown peridot revealed an unexpected inclusion scene quite different from the common inclusions found in green peridot.
