TEKTITES 451 Figure 10 (A C) Microtektites and (D) microcrystite (clinopyroxene microspherule), all from Deep Sea Drilling Project 689, Maud Rise, Weddell Sea The microtektites are equated with the North American strewn field and the microcrystite is equated with the Popigai impact structure, northern Siberia Reproduced with permission from Glass BP and Koeberl C (1999) Ocean Drilling Project Hole 689B spherules and Upper Eocene microtektite and clinopyroxene bearing spherule strewn fields Science 34: 197 208 during the Oligocene 29 million years ago from two small craters (named BP and Oasis) that are situated about 100 km to the west A minute fragment of an iron meteorite has been found with these glass objects The glass was used to make Acheulian scrapers Mount Darwin Glass Irregular masses of anomalous glass have found on the surface in western Tasmania and near Mt Macedon in Victoria The glass mass is layered, not unlike Muong Nong-type tektites, but the silica content is much higher (88%, compared to 73%) Radiometric dating indicates formation 0.73 Ma, but the occurrence of these masses clearly has nothing to with australites A 1000-m-diameter crater has been recognized close to the occurrences of these glass objects in Tasmania, but there is no evidence of impact on excavation, though this site may be the source of the glass The similar glass found at Mt Macedon, across the Bass Strait, 560 km to the north, is unexplained Zhamanshinites and Irghizites Slags and glasses have been reported from the 13.5-km Zhamanshin impact structure in Kazakhstan, north of the Aral Sea (see Figure 2), overlying Palaeogene country rock The best radiometric age derived dates these objects to 1.09 Ma Zhamanshinites contain rock fragments and are impactite glasses Irghizites occur within the bounds of the crater structure, not in an external strewn field, and are composed of small ‘micro-irghizite’ particles, welded together The silica content of the irghizites is 72–79%, not unlike that of tektites, but the water content is slightly higher The interest in these objects is that they may represent the separation of microtektites at source Urengoites Three fragments of tektite-like glass have been found buried in Siberia at two sites 40 km apart (see Figure 2); based on radiometric dating, these urengoites were formed at 22–24 Ma The Eltanin Glasses The 25-km-wide Pliocene Eltanin structure on the floor of the southern Pacific Ocean (see Figure 2) has both associated minute fragments of a mesosiderite (stony iron) meteorite and microscopic glass spherules; these objects have been recovered in piston