PHYSICOCHEMICAL STRUCTURAL CHARACTERIZATION OF AMBERS FROM DEPOSITS IN POLAND

The physical and chemical properties of 8 samples of amber from differ ent localities in Poland (Baltic Coast, Belchatow Tertiary brown coal, and Jaroszow clay mine) were investigated by N-2 sorption at 77 K, po sitron annihilation spectroscopy for chemical analysis (PASCA) and by organic geochemical methods (FT-IR, H-1 and C-13 NMR, GC, and GC-MS). The porosity of the ambers as determined by PASCA consists of narrow m icropores with diameters ranging from 0.8 to 0.9 nm and a volume 0.025 cm(3) g(-1). In the external eroded part of the amber samples (rind) the concentration of pores where positronium atoms can form is lower a nd consists of approximately 1/2 the concentration as in their interio r. Values of pore parameters determined from sorption of N-2 are compa rable with those found by the PASCA method. The average diameter of po res ranges from 2 to 12 nm, while their volume varies from 0.018 to 0. 048 cm(3) g(-1). The chemical character of the ambers is similar based on FT-IR spectroscopy. However, noticeable differences in concentrati ons of ester and hydroxyl groups are observed in both exterior and int erior regions, where the abundances of the ester groups are lower in t he exterior rind. The proportion of organic material extractable with chloroform-methanol (1:1, v/v) ranges from 15 to 50% and correlates in versely to the average reflectances (R(r)) of polished amber surfaces which range from 1.7 to 0.1%. These variations are attributed to diffe ring concentrations of oxygenated groups in the respective amber sampl es. The FT-IR spectra of the non-polar fractions (NP) from the extract s resemble the spectra of the source ambers. However, the intensities of the absorbance for the hydroxyl group are much lower, while absorba nces for exomethylene groups are not present. The H-1 and C-13 NMR dat a of NP fractions showed a complex diversity of components in mixtures with different relative concentrations but predominantly aliphatic in character for the respective samples. GC and GC-MS analyses of these fractions revealed that they are comprised of a mixture of compounds t ypical for Baltic amber but with variable relative concentrations. Two groups of compounds are found to be common to all NP fractions. The f irst is a minor concentration of homologous n-alkanes with a character istic Gaussian distribution in the range from C-22 to C-32 and maximiz ing at C-26-C-27. In addition C-22 is characteristically slightly high er in concentration compared to C-23. The second group of compounds is comprised of succinates with methyl, fenchyl, bornyl and isobornyl al cohols. The composition of these diesters revealed the same equilibriu m ratio between compounds with fenchyl, bornyl and isobornyl alcohols in all NP fractions. We suggest an early enzymatically controlled (bac terial) process in the formation of succinates during resin diagenesis from the biotic precursors, yielding the same characteristic ratio of the respective succinates in these ambers. These results show that al l the ambers analyzed here fall into a common class of fossil resin, s uccinite (class Ia) independent of the sample location in Poland. Copy right (C) 1996 Elsevier Science Ltd.