PETROGRAPHIC CHARACTERISTICS OF SOME TEKTITES FROM WESTERN BELIZE

Doubly polished thin sections of three Belize tektites show: (1) Rare inclusions of lechatelierite (high-T amorphous SiO₂ derived from quartz and in some instances including quartz regions) and quartz (including embayed grains, quartz grains showing incipient melting that was quenched and quartz with toasted patches and ballen texture). Most lechatelierite in our thin sections is embayed (on the margins and/or within the grain) and contains at least some brown regions that appear to have been toasted. Ballen is present in some lechatelierite grains and some grains contain regions of apparently unaltered quartz. Lechatelierite grains average c. 50 µm; quartz average c. 40 µm. They range from pristine and apparently unaltered quartz to embayed grains showing incipient melting and toasting. (2) Rare opaque grains tend to occur near lechatelierite and quartz inclusions and tend they to be significantly (~50%) smaller than typical lechatelierite or quartz grains. Opaque grains are usually black, but some have a slight red hue on the periphery. Opaque grains were not observed in incipient melting situations and are not embayed. Magnetic measurements indicate that among Belize tektites in general a few specimens contain a significant amount of magnetite inclusions, with concentrations up to 200 ppm. (3) Vesicles are rare components of the three specimens studied. The average size is 0.6 mm, but range 0.1-0.8 mm. Vesicles are round and were approximately evenly distributed throughout. (4) Bubbles we noted are not vesicles. Bubbles are on average about 0.1 mm or less and tend to occur in clusters of a few to more than 20, and the clusters are in direct physical contact with lechatelierite and ballen quartz grains. (5) Schlieren in our three pale yellowish brown tektites was pervasive but very subtle and not folded. Adjacent individual flow bands or streaks typically were not profoundly different in color, grain or vesicle content, vesicle shape, or translucence.