Magnetic measurements of glass from Tikal, Guatemala: Possible tektites

Abstract

Abstract. Certain glass nodules found at the archeological site at Tikal, Guatemala, have been considered as possible tektites. To test this possibility, magnetic studies have been made on three of the glass specimens. These specimens are similar to tektites, both visually and also because they contain very little Fe 3+ as detected by M6ssbauer spectroscopy. The magnetic Curie constants are similar in magnitude to those found for normal tektites but show some variation from point to point in the same specimen. This variation reflects an inhomogeneity in the iron concentration. The Fe 2+ calculated from the Curie constants accounts for most of the iron. The temperature-independent component of the total dc magnetic susceptibility is several times higher than that found in tektites from other strewn fields. The high values can be explained if the glass contains metallic iron spherules with Fe in the parts per million range and/or a ferromagnetic component which does not saturate in a low magnetic field. The magnetic properties resemble those of Muong Nong type tektites and suggest that the Tikal glass specimens are tektites of the Muong Nong type. IntroductionEsserie et al. [1987] have reported microprobe analyses of 11 unworked nodules of olive-green vesicular glass found in the Mayan city of Tikal, Guatemala. Their analysis indicated that the glass had an andesitic composition. They suggested that because of the complete lack of crystallites these specimens would be highly anomalous if they were andesitic obsidians. Because it is unlikely, and surely unique, that these specimens were derived from andesitic obsidian, Esserie et al. [1987] further suggested that the specimens may be impactites from a terrestrial andesitic source rock. Later, Moholy-Nagy and Nelson [1990] reported on a study of some 30 obsidian artifacts from the same area. In an effort to trace the source of the obsidian they analyzed the specimens for 10 different elements using X-ray fluorescence. One of the specimens (their number 1589) was an unworked brownish-green glass nodule that had a composition distinctly different from the other obsidian artifacts. The Fe, Ti, and Sr concentrations were higher, and the Rb and Nb concentrations were lower than those determined for any of the other obsidian fragments. The obsidian fragments could all be related to known local quarries, while specimen 1589 was of unknown origin and from a source of more andesitic composition. The surface of the nodule was pitted, and the glass was remarkably free of crystallites. Because of these characteristics it was suggested that this specimen might We report here a magnetic study on three of the specimens described in the above studies and designated as 12T-451/79, 20M-97B/41 (same as Moholy-Nagy and Nelson [1990] specimen 1589), and 24F-26/11 (hereinafter referred to as 12T, 20M, and 24F) in an attempt to confirm them as true tektites. Senfile and Thorpe [1959] have shown that magnetic properties can be used to distinguish tektites from obsidian glass. Obsidians ...

Impact glasses from Belize represent tektites from the Pleistocene Pantasma impact crater in Nicaragua

“…Variability is significantly lower within than between samples. The good match between the scarce data for Tikal glass 14 , 15 and our belizite data is shown in supplementary Fig. 3 .…”

“…In archeological excavations of the Mayan city of Tikal (North Guatemala; Fig. 1 ), tektite-looking glasses were identified 14 , 15 . Based on their andesitic composition (i.e., different from obsidian artifacts), low water content (≈80 ppm), and low Fe 3+ concentration (from Mössbauer spectroscopy and magnetic properties) they were proposed to be tektites.…”

“…1 , Supplementary Note 2 ) and has not increased through time, despite intensive searches since 1990 by J.C. and other researchers, including locals trained by J.C. The inclusion in the inventory of impact glasses recovered in Maya excavations from Tikal 14 , 15 may extend this size to 80 km. However, the discovery of such obsidian-looking glass in these archeological excavations may either be interpreted as being of local natural source or from the trade of this rare material from a Mayan city within the Belize strewn-field.…”

Non-Magmatic Glasses

“…Besides these four well-known tektite strewn fields, recently, other two have been proposed, one from central American (Belize glasses), and the second from Uruguay (uruguaites) (Ferrière et al 2017;Giuli et al 2014b;Povenmire et al 2011;Povenmire & Cornec 2015;Senftle et al 2000). The chemical composition of tektites is fairly homogeneous within the same strewn-field, and also among the four strewn-fields the chemistry of all distal ejecta shows that these glasses are aluminosilicates with high SiO2 contents and alkalis depleted (see Table 1).…”

Magnetic Properties and Redox State of Impact Glasses: A Review and New Case Studies from Siberia

“…All those samples show negligible saturation magnetization (M S , measured on a high field Curie balance using 1-10 mg samples, with a sensitivity better than 10 -4 Am 2 /kg). Several other glasses (Georgiaite, Australasian microtektite, Tikal glass) were measured later using the same technique [16][17][18].…”