Examination of amber and related materials by NMR spectroscopy † Joseph B. Lambert, a * Jorge A. Santiago-Blay, b Yuyang Wu c and Allison J. Levy a Examination of the solid-state 13 C and solution 1 H NMR spectra of fossilized resins (ambers) has generated five groupings of materials based on spectral characteristics. The worldwide Group A is associated with the botanical family of the Araucariaceae. The worldwide Group B is associated with the Dipterocarpaceae. Baltic amber or succinite (Group C) is related to Group A but with a disputed conifer source. Amber from Latin America, the Caribbean, and Africa is associated with the Fabaceae, the genus Hymenaea in particular. The minor Group E contains the rare fossil polystyrene. The spectra of jet indicate that it is a coal-like material with a rank between lignite and sub-bituminous coal. Copyright © 2014 John Wiley & Sons, Ltd. Keywords: amber; copal; jet; paleobotany; plant exudates; resins Introduction The material widely known as amber, or by a similar term in the English, Romance, and Arabic languages, has been collected, mined, worked, and traded at least since Neolithic times in Europe and has been in use since the Upper Paleolithic (ca. 20 000 BP). It has been known as Bernstein (‘the burning stone’) in the Germanic languages, as ηλεκτρον (electron, meaning ‘shining sun’, from which all electronic terms are derived) in the Greek and Russia (элекрон) languages, and as jantar (‘resin’) in the Slavic languages. Even in its raw form, amber has an attractive appearance that undoubtedly led to its uses. As a gemstone, it is almost unique, as its structure is organic. Opaque or translucent, amber varies naturally from nearly colorless or light yellow to gold or the classic dark orange–yellow color (‘amber’), grading to red, brown, black, or even shades of green and blue. Color is not useful as an indicator of either geographic source or paleobotanical origin. The cause of color is not from the organic structure but either from inorganic impurities or from a purely optical effect. The deep browns and blacks may be from trace amounts of reduced (ferrous) iron. From ancient times to today, amber has found uses as jewelry, objects of art (boxes and cups), utilitarian objects (smoking mouthpieces and lent balls because rubbing generates static electricity), medicine, incense, flavoring, preservatives, fragrances, a precursor to varnish, and even a building material. [1–5] Amber originated from tripenoid resins exuded by certain trees millions of years ago. [6] Maturation over geological time through polymerization, cross-linking, and oxidation resulted in a robust, rock-like product that is stable to moderate temperatures and chemical conditions. Amber is partially soluble in some organic solvents, but, as a predominantly hydrocarbon material, it is insolu- ble in water. Indeed, the early sources of European amber were the shores of the Baltic Sea. Most archeological artifacts from biological sources, such as paper, textiles, or skin, decay rapidly into soil humus and in some cases (over long periods of time) become fossil fuels, but the cross-linked, polymeric structure of amber allows it to survive. Along with jet, a product of the woody portions of trees, [7] amber is classified as a mineraloid. Such materials are noncrystalline and also include inorganics such as obsidian and opal and composite organic/inorganics such as pearls. Amber and jet are the principal organic mineraloids, although some authors include liquids like petroleum. The term amber is used commonly to refer to plant resins that have undergone geological maturation over millions of years, but originally, the term specifically applied to those materials found around the Baltic Sea. Herein, we use the term in its most general sense and do not distinguish it from other terms such as resinite or fossilized resin. [8] Amber typically dates to the Tertiary and Cretaceous periods (3–140 million years ago, or Ma), although rarely they are found in Jurassic, Triassic, and Carboniferous deposits up to about 320 Ma. [9] Younger or less matured plant resins, called copals, are partially polymerized, cross-linked, and oxidized after hundreds or thousands of years or up to a million years. It is difficult to distinguish amber from copal visually, although the latter generally is much softer and is almost entirely soluble in organic solvents such as chloroform, whereas the former is partially to poorly soluble. As a result, amber has been used commonly for jewelry, but copal for ceremonial or medicinal purposes such as incense. Langenheim [6] has emphasized the difficulty of dis- tinguishing amber from copal, which she calls subfossil or ancient resin (as distinguished from modern resin, found on or under living trees); the term semifossilized also is used. Herein, we use the term copal in general for immature or partially polymerized fossil resins. * Correspondence to: Joseph B. Lambert, Department of Chemistry, Trinity University, San Antonio, TX 78209, USA. E-mail: jlambert@trinity.edu † This article is published in Magnetic Resonance in Chemistry as a special issue on the NMR in Cultural Heritage by Donatella Capitani and Noemi Proietti (Istituto di Metodologie Chimiche, CNR Area della Ricerca di Roma, Monterotondo (Rome) Italy). a Department of Chemistry, Trinity University, San Antonio, TX, USA b Department of Paleobiology, National Museum of Natural History, Washington, DC, USA c Department of Chemistry, Northwestern University, Evanston, IL, USA Magn. Reson. Chem. 2015, 53,2–8 Copyright © 2014 John Wiley & Sons, Ltd. Special issue review Received: 2 June 2014 Revised: 4 July 2014 Accepted: 11 July 2014 Published online in Wiley Online Library: 31 August 2014 (wileyonlinelibrary.com) DOI 10.1002/mrc.4121 2