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Abstract--The Rokle bentonite deposit is part of an accumulation of argillized volcanoclastic rocks in the Tertiary stratovolcanic complex of the Doupovsk6 Mountains east of Karlovy Vary (Carlsbad), about 100 km westnorthwest of Prague, Czechoslovakia. The arenite basalt ash was originally composed of hyaloclasts and subordinate biotite. The following types of montmorillonite aggregates were produced during the alteration of the ash in a stagnant, lacustrine environment: (1) extremely fine-grained microcrystalline aggregates that have honeycomb textures and that replace the original hyaloclasts, and (2) coarse crystalline aggregates that have more open honeycomb textures and that fill pores and cracks in altered hyaloclasts and in pumice vesicles. Both types of aggregates have the same chemical composition according to energy dispersive X-ray analysis.Montmorillonite, separated as the < 1-gm size fraction from olive gray bentonite, has the following crystallochemical formula: (Ko.09Nao.02Cao.29Mgo.lo) (AIE.43Fe3+l.osFe2+o.oosMnE+o.oosMgo.50) (Si7.62A10.38) O2o(OH)4. Biotite was apparently stable during the alteration of the hyaloclasts. Anatase and possible accessory heulandite-clinoptilolite were also formed in small amounts, but were not observed by scanning electron microscopy. Goethite is the youngest oxidation product in some parts of the bentonite. Minute fragments of sodium-rich plagioclase, potassium feldspar, quartz, and muscovite are ubiquitous accessories of the original hyaloclasts. Together with kaolinite, they formed from the underlying fresh or kaolinized orthogneiss.Abstrakt--Lo~isko bentonitu Rokle je sourfisti srrie argilizovanych vulkanoklastick~ch akumulaci v tercirrnim stratovulkanickrm komplexu Doupovsk~ch hor v~chodn6 od Karlov~ch VarY, asi 100 km z/tpadoseveroz~tpadn6 od Prahy, Ceskoslovensko. Psamitov~ bazaltov') popel byl sloven z hyaloklastfl a biotitu jako pod~adn6 sou~istky. B6hem p~'em6ny popela ve stagnujicim jezernim prost~edi se vytvoi'ily nhsledujici typy agreg~tfl montmorillonitu: (1) extr6mn6 jemnozrnn6 mikrokrystalick6 agregfity s pl~is-tevnou mikrotexturou, kter6 nahradily pfivodni hyaloldasty; (2) hrub~ji krystalick6 agregaty s plfistevn~mi mikrotexturami vice otev~en~mi, kter6 vyplnuji pory a trhliny v p~em6n6n~ch hyaloklastech a tak6 vesikuly v pemze. Oba typy agreg~tfi s rflznou mikrotexturou maji stejn6 chemick6 slo~eni, zji~t6n6 energiovou dispersni anal~zou paprskfl X.Montmorillonit, separovanr velikostni frakce pod 1 #m z olivov6 ~ed6ho bentonitu, m~i n~sledujici krystalochemick~ vzorec: (Ko,09Nao,02Cao.29Mgo, ~ o)(A12,43Fe3+ 1,05Fe2+o,oosMn2+o,oosMgo,so)(Si7,62Alo.3s)O20(OH)4.Biotit zfistal stabilni brhem p~emrny hyaloklastfi. Anatas a.pravdrpodobn~ akcesorick~ hevlandit-klinoptilolit (podle jedin6 velmi slab6 rentgenov6 reflexe 8,85 A) vznikly jako malfi p/imrs, av~ak nebyly pozorovfiny pod SEM. Goethit je nejmlad~i oxidarni produkt v nrkter~ch partiich bentonitu. Drobn6 filomky plagioklasu bohatrho sodikem, draselnrho ~ivce, k~emene a muskovitu jsou v~udyp/Stomn~m...

SUMMARY. The volatilities of SiO~, Na~O, and Fe~Oa x increase with increasing thermal function within the range 1600 to 2100 ~ during the melting of a sandy-silty clay. The remaining melt is to some extent enriched in Al~O3, K,O, CaO, and MgO. Chemical analyses of the sandy-silty clay, of the glasses melted from the latter, of the silicate material evaporated and newly condensed and their correlation with increasing thermal function and bulk density of glasses, as well as with the hitherto known quantitative data on moldavites, testify to the fact that in moldavites evaporated and newly condensed silicate material substantially prevails over material that passed directly from a solid to a fluid state. Evaporation of the silicate material from the rocks of the impact crater caused a significant change in relations between major oxides compared to the original relations in the source rocks. Thus, the hypothesis that tektites are directly remelted rocks of the Earth's crust, based on over-all chemical similarities of tektites and some rocks in major oxides, appears incorrect.MOLDAVITES are inhomogeneous silicate glasses belonging to tektites; they occur in southern Bohemia and Moravia, Czechoslovakia. Studies that contributed to a more detailed knowledge of moldavites were made by

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SUMMARY. I666 moldavites from 19 localities in Bohemia and 617 moldavites from IO localities in Moravia were measured to yield parameters L (length), B (breadth), and T (thickness). A digital computer was programmed to calculate values T/L, (L--B)/(L--T), andThe data obtained permit an interpretation that localities of moldavites with low average sphericity contain less heated material. Less heated and thus more viscous glass could have flown along shorter trajectories (Bohemia). More heated glass was ejected to geographically more distant places (Moravia) or travelled along reIatively long steeper trajectories (several localities in Bohemia).MOLDAVITES from localities in Bohemia are mostly drop-like, flat or elongate, whereas moldavites from localities in Moravia are frequently massive to spheroidal. Among the moldavites in Bohemia, complete forms are rare, which can be explained by an easier breakage of flat or rod-like forms with a relatively low sphericity. Massive torspheroidal moldavites from Moravia yield more complete forms. Most fragments, irrespective of their present shape, indicate sphericity of the original forms, so that average values of a large number of measurements characterize individual localities.Shape, colour, weight, and surface features of several thousand moldavites were described qualitatively by Bou~ka, Faul, and Naeser (I968). They concluded that 'Shapes of moldavites show significant differences among localities, but no trends appear, it is possible to state only that the moldavites from Moravia have mainly round shapes. Moldavites could not have been transported more than a few km by water, and the original strewn fields must have been very small.' Konta and Mr~tz (1969) studied the relationship between chemical composition, bulk density, and sphericity and hypothesized a relationship between sphericity of moldavites and viscosity of the hot glass and the magnitude of thermal energy liberated in different impact areas.This study was aimed at exploiting the shape analysis of moldavites to verify the assumed mutual position of the source area (Ries Crater) and the strewn fields. Shape parameters of tektites such as sphericity, which have not been explored yet, were analysed quantitatively. The shape parameters of moldavites were expressed analogously to those of fragments used in petrology of coarse clastic sediments (Sneed and Folk, I958; Zingg, 1935). In the course of a secondary relatively short transport by 9