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Lot 260
Limonite in Topaz--"A Member of the 100 Carats Club"
7 December 2016, 10:00 PST
Los AngelesUS$10,000 - US$15,000
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Limonite in Topaz--"A Member of the 100 Carats Club"
Burma
In the Summer of 1987, The Gemological Institute of America (GIA) published an article in their journal that discussed the difference between rutilated topaz and limonated topaz. The needle-like inclusions in so-called "rutilated topaz" are actually limonite staining that fills hollow tubes in the topaz. In fact rutile is not known to crystallize at all in topaz in a ribbon-like form that would produce effects similar to those in rutile quartz. Limonite is quite a different mineral from rutile. Rutile is titanium dioxide and has an exceptionally high refractive index, much higher than diamond. Limonite is actually not itself a true mineral, rather it is a combination of iron oxide minerals such as goethite and lepidocrocite. Typically yellow-brown in color, limonite is used as the basis for the natural earth pigment ochre. Thus the name "rutilated topaz" is a misnomer, clearly derived from the better-known "rutilated quartz". One can only surmise that the name persists because its true name of "Limonite-stained Topaz" would have greater difficulty in gaining public acceptance. The present stone is a rare near-colorless topaz, polished into a large double cabochon of lenticular form. Large areas of the topaz have nearly optically clear transparency and the inclusions of limonite stand out in high relief against the topaz. Weighing approximately 104.45 carats and measuring 32.24 x 10.25mm
In the Summer of 1987, The Gemological Institute of America (GIA) published an article in their journal that discussed the difference between rutilated topaz and limonated topaz. The needle-like inclusions in so-called "rutilated topaz" are actually limonite staining that fills hollow tubes in the topaz. In fact rutile is not known to crystallize at all in topaz in a ribbon-like form that would produce effects similar to those in rutile quartz. Limonite is quite a different mineral from rutile. Rutile is titanium dioxide and has an exceptionally high refractive index, much higher than diamond. Limonite is actually not itself a true mineral, rather it is a combination of iron oxide minerals such as goethite and lepidocrocite. Typically yellow-brown in color, limonite is used as the basis for the natural earth pigment ochre. Thus the name "rutilated topaz" is a misnomer, clearly derived from the better-known "rutilated quartz". One can only surmise that the name persists because its true name of "Limonite-stained Topaz" would have greater difficulty in gaining public acceptance. The present stone is a rare near-colorless topaz, polished into a large double cabochon of lenticular form. Large areas of the topaz have nearly optically clear transparency and the inclusions of limonite stand out in high relief against the topaz. Weighing approximately 104.45 carats and measuring 32.24 x 10.25mm