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Lot 8461
Iridescent Andradite Garnet
3 December 2006, 11:00 PST
Los AngelesUS$1,500 - US$2,000
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Find your local specialistIridescent Andradite Garnet
Sierra Madre Mountain, Sonora, Mexico
A chemical cousin to demantoid, which is colored by chromium, is this relatively unknown variety of andradite garnet, originating from a new locality in Mexico. Grossular and andradite garnet form a continuous series with each other, with the aluminum and iron ions replacing each other. The high degree of intermixing that takes place within the garnet family contributes to the great number of garnet varieties.
The difference in the chemical compositions of the members of the series, together with variations of temperature and pressure of the environment where crystallization takes place can produce this unusual iridescent garnet. The iridescence occurs through the incorporation of extremely thin layers of grossular in andradite’s isometric structure. The slight differences in the refractive indices of the layers of the two minerals affect the light reflected from within the stone causing the spectral effect.
The present example is a cabochon cut in a novel style with angular facets to best exhibit the beautiful blues and green inherent in the stone. This is a valued connoisseur’s gemstone which is also a published stone. Weighing approximately 8.52 carats and measuring 15.2 x 11.3 x 5.5mm
A chemical cousin to demantoid, which is colored by chromium, is this relatively unknown variety of andradite garnet, originating from a new locality in Mexico. Grossular and andradite garnet form a continuous series with each other, with the aluminum and iron ions replacing each other. The high degree of intermixing that takes place within the garnet family contributes to the great number of garnet varieties.
The difference in the chemical compositions of the members of the series, together with variations of temperature and pressure of the environment where crystallization takes place can produce this unusual iridescent garnet. The iridescence occurs through the incorporation of extremely thin layers of grossular in andradite’s isometric structure. The slight differences in the refractive indices of the layers of the two minerals affect the light reflected from within the stone causing the spectral effect.
The present example is a cabochon cut in a novel style with angular facets to best exhibit the beautiful blues and green inherent in the stone. This is a valued connoisseur’s gemstone which is also a published stone. Weighing approximately 8.52 carats and measuring 15.2 x 11.3 x 5.5mm
Footnotes
Accompanied by a copy of the article entitled “Iridescent Andradite: Garnet Meets Opal”, from Modern Jeweler magazine, July 2007, where the present 8.52 carats stone was illustrated and featured.