Dominican,baltic Sea And Myanmar Amber Characteristics And Mineral Deposits Study

Amber,the fossilized forms of resinite produced by various plants,has been of great interest to gemologist,botanist,entomologist and paleontologists because of its high commercial value and archaeologicalimportance.Dominican Republic,Myanmar and the Baltic Sea are three important Amber-bearing deposits in the world,withgreatgemological and mineralogical significance.In this paper,we summarized the spectral discriminating characteristics of ambers in three areas and analyze the causes of their differences in spectrum from the perspective of structure and composition.Then we studied formation age and deposit conditions and their effect on the organic structure of Dominican amber.The test methods include Infrared spectroscopy,Raman spectroscopy,zircon U-Th-Pb isotope analysis,X-ray powder diffraction,scanning electron microscopy and iron isotope analysis.In addition,the internal structure of Baltic beeswax and Burmese opaque amber were observed,and the formation mechanism was explored.Spectroscopic studies indicate thatbasic skeletons of ambers from the deposits of Dominican Republic,Burma and Baltic Seaare aliphatic structure,whose spectral characteristics show the absorption peaks caused by C-Hvibrations.However,refineddifferencesinlocationandintensityofabsorptionpeakscouldbeidentified,which locate(1)in the range of 1740?1690cm^-1of the infrared spectrum:Dominican ambers have strong 1695cm^-1and weak 1724cm^-1peaks,Baltic Sea ambers have a strong1735cm^-1peak,and Burmese amber strong 1726cm^-1and weak 1695cm^-1peak;(2)between 1300cm^-1and 1000cm^-1:strong band at 1242cm^-1in spectra of Dominican ambers,“Baltic shoulder”in that of Baltic ambers and strong peaks at 1157cm^-1in spectra of Burmese ones;(3)atbands of 3086cm^-1,1645cm^-1and 888cm^-1,which are present in the infrared spectra of the Dominican and Baltic ambers,and absent in those of Myanmar amber;(4)in IR spectrum 3300?2800 cm^-1range and intensity ratio of 1377cm^-1and 1454cm^-1peaks.The above differences can be used as the basis for the identification of amber origin in actual detection.Amber maturity and composition are the cause of the difference in the above infrared spectra.The maturity of amber samples listed in sequence,from high to low,are burmite,Baltic ambers and Dominican ambers.Age and deposite conditions have influence on amber maturity,and botanic origin or depositional environment may effect the organic composition.Zirconsfrom sedimentary rocksin the Dominican amber-bearingdepositshow rhombic zoning under cathodoluminescence(CL),and the Th/U ratio in the U-Pb test is more than 0.2,typical of amagmatic origin.U-Pb ages of the zircons in northern areafall into 86?88Ma and 50?54Ma,and ones in the eastern area yield an age of 118Ma.The Zircons are more likely derived from Greater Antilles arc magmatism in the Caribbean region,based the the time and geographical location of magmatic activity.Moreover,Dominican amber was probably formed at(but not earlier than)50.9±1.7Ma.Pyrite and quartz are the majorcomponents on the surface of Dominican ambers.Morphology is dominated by framboid pyrite,with diameter between 10?17?m,formed by a large number of pyrite microcrystals of octahedral,spherical and pentagonal icositetrahedral.Small amount of euhedral crystals and tubular crystals occur as well.Iron isotope of pyrite indicates continental shelf sedimentary origin.Beeswax-amber appears semitransparent to opaque is a valuable kind of Baltic amber.A large amount of nanoscalebubbles occur under the scanning electron microscopy(SEM),which result in the poor transparency.Low-temperature condition at the both processes of secretion of resins and burial to fossilize into amber is inferred to play a positive role on formation and existence of bubbles inside of Beeswax-colored amber.Gas bubbles are also found inside of the opaque amber from Myanmar,with well-crystallized cubic Na Cl crystals.The reason for the presence of inorganic minerals in amber still needs further study.