From mastodon ivory to gemstone: The origin of turquoise color in odontolite
-
Ina Reiche
,
Colette Vignaud
Abstract
Heat-induced color changes of fossilized Miocene mastodon ivory (13-16 Ma) have been known at least since the Middle Ages. Cistercian monks are believed to have created odontolite, a turquoise- blue “gemstone,” by heating mastodon ivory found in Miocene geological layers next to the Pyrrenean chain, France, to use it for the decoration of medieval art objects. This material has been the object of investigations of famous European naturalists and gemmologists, among them Réaumur (1683-1757). Although vivianite [Fe3(PO4)2·8H2O] is the commonly accepted coloring phase supposed to appear when heating fossilized mastodon ivory, our previous spectroscopic studies using PIXE/PIGE and TEM-EDX demonstrated that the chemical composition of collection odontolite and heated mastodon ivory corresponds to well-crystallized fluorapatite [Ca5(PO4)3F] containing trace amounts of Fe (230-890 ppm), Mn (220-650 ppm), Ba (160-620 ppm), Pb (40-140 ppm), and U (80-210 ppm). No vivianite has been detected.
To provide new insights into the physico-chemical mechanism of the color transformation of fossilized ivory, we used the combination of UV/visible/near-IR reflectance spectroscopy, time-resolved laser-induced luminescence spectroscopy (TRLIF), and X-ray absorption near-edge structure (XANES).
Contrary to what had formerly been described as the color origin in odontolite, our study has conclusively identified traces of Mn5+ by UV/visible/near-IR reflectance spectroscopy, TRLIF, and XANES inside the fluorapatite. Thus, odontolite owes its turquoise-blue color to Mn5+ ions in a distorted tetrahedral environment of four O2- ions. XANES also demonstrated oxidation of disordered octahedral Mn2+ ions to tetrahedral Mn5+ species in apatite during the heat process. So we give the first evidence of the real color origin in odontolite.
© 2015 by Walter de Gruyter Berlin/Boston
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Artikel in diesem Heft
- First-principles modeling of the infrared spectrum of kaolinite
- Determination of the limiting fictive temperature of silicate glasses from calorimetric and dilatometric methods: Application to low-temperature liquid volume measurements
- Enthalpies of formation of tremolite and talc by high-temperature solution calorimetry – a consistent picture
- Evidence for an I2/a to Imab phase transition in the silica polymorph moganite at ~570 K
- Thermal decomposition of rhombohedral KClO3 from 29–76 kilobars and implications for the molar volume of fluid oxygen at high pressures
- High-pressure behavior of clinochlore
- Structure and elasticity of wadsleyite at high pressures
- Determination of the fluid–absent solidus and supersolidus phase relationships of MORB-derived amphibolites in the range 4–14 kbar
- F-rich phlogopite stability in ultra-high-temperature metapelites from the Napier Complex, East Antarctica
- Instability of Al2SiO5 “triple-point” assemblages in muscovite+biotite+quartz-bearing metapelites, with implications
- Stability of osumilite coexisting with spinel solid solution in metapelitic granulites at high oxygen fugacity
- Geikielite exsolution in spinel
- Aeromagnetic anomalies, magnetic petrology, and rock magnetism of hemo-ilmenite- and magnetite-rich cumulate rocks from the Sokndal Region, South Rogaland, Norway
- Minor element chemistry of hemo-ilmenite and magnetite in cumulate rocks from the Sokndal Region, South Rogaland, Norway
- Crystal structure analysis of synthetic Ca4Fe1.5Al17.67O32: A high-pressure, spinel-related phase
- Crystal structure of phase X, a high pressure alkali-rich hydrous silicate and its anhydrous equivalent
- Fluoro-edenite from Biancavilla (Catania, Sicily, Italy): Crystal chemistry of a new amphibole end-member
- Description and crystal structure of turtmannite, a new mineral with a 68 Å period related to mcgovernite
- The crystal structure of low melanophlogite
- Crystal structures of Na and K aluminate mullites
- From mastodon ivory to gemstone: The origin of turquoise color in odontolite
- Letters. Elasticity of single-crystal calcite and rhodochrosite by Brillouin spectroscopy
- Ikaite, CaCO3·6H2O: Cold comfort for glendonites as paleothermometers
