Virgil E. Barnes

Macusanite Occurrence, Age, and Composition, Macusani, Peru

Macusanite, originally believed to be a type of tektite because of its sculpture, is shown to be related to sillar of the Macusani region, Peru. K-Ar measurements establish identical Pliocene ages (4.2 m.y.) for macusanite and sillar and relate these deposits to the extensive ash flows of the southern Andes. These rocks are unique for glassy rocks in that lithium, boron, and arsenic contents are very high; cesium, rubidium, tellurium, fluorine, and tin are higher than normal; zinc, copper, chromium, and zirconium are lower than normal; and high-alumina minerals such as andalusite are present.

Variation of petrographic and chemical characteristics of indochinite tektites within their strewn-field

Abstract Normal indochinites in the central part of their strewn-field are slightly more siliceous, have slightly lower refractive indices, contain fewer and smaller lechatelierite particles and bubbles, and more of the bubbles are spherical. These characteristics of normal indochinites vary in a manner which indicates that a central area of higher temperature existed at the time of indochinite formation. These observations are supported by sixteen new chemical analyses, eight of normal and eight of Muong Nong-type indochinites, and petrographic examination of 288 plates cut from as many specimens. Tektite characteristics in two other strewn-fields examined also vary systematically. The center of the moldavite strewn-field probably is in Moravia or eastward, rather than westward toward the Ries Kessel. The center of the bediasite strewn-field probably is in the vicinity of their southwesternmost presently-known occurrence or farther southwest.

Properties of tektites pertinent to their origin

Abstract Theories of the origin of tektites are examined to see if they explain the following critical properties: chemical properties, lechatelierite particles, two periods of melting, flow structure, shapes and sizes, and distribution of age. A volcanic origin either from the earth or the moon cannot explain the above properties; neither can an origin from lightning, or as impactites from the moon, or from collisions of asteroids with each other. The impact theory of Urey can explain the tektites if the molten rock was thrown beyond the earths atmosphere and was remelted upon its return. The absence of partially fused tektites is against such a hypothesis. The formation of tektites by the destruction of a planet similar to the earth should not be overlooked.

Petrology of moldavites

Abstract During the systematic petrological examination of 311 Bohemian and 130 Moravian moldavites, layered Muong Nong type specimens were found to be fairly common. In these layered forms mineral grains which appear to be detrital were found in one specimen, another contains thin bubbles of irregular angular outline, and other specimens contain rayed bubbles and elongate ray clusters. Schlieren and objects of both higher and lower refractive index than the enclosing glass occur in splash form moldavites, and lechatelierite particles of varied shape and surface configuration are found in both splash and layered forms. When values for petrological properties of moldavites (refractive index, specific gravity, lechatelierite abundance, lechatelierite size, lechatelierite shape, bubble abundance, bubble size, bubble shape, strength of flow structure, strength of flow structure strain, and strength of overall strain) are averaged by groups of localities and plotted on a map of Czechoslovakia, a systematic direction of variation is found for the Bohemian part of the strewn-field but not for the Moravian part. On the basis of these properties for the strewn field as a whole, the central part of the strewn-field is postulated to be in the vicinity of the Moravian area of moldavite occurrence. Local melting probably took place over an area at least twice the diameter of the present known area of moldavite distribution.

New investigations of the strewn field of Libyan desert glass and its petrography

Twenty-six specimens of Libyan Desert glass were collected from the westernmost area of Libyan Desert glass occurrence during a joint expedition, 30 May to 5 June, 1971, of The University of Libya and The University of Texas. The Oasis circular structure, a suspected astrobleme southwest of the glass site, was also visited. In the glass, included minerals are partially altered through shock and temperature effects; microprobe analysis confirms one of these minerals as zircon and indicates that another is the elbaite variety of tourmaline. Tourmaline of the elbaite variety and zircon were also identified in a thin section of an analyzed sample of high-silica (99.6%) Nubian Sandstone collected in the area of glass occurrence. This silica content is higher than that of any Libyan Desert glass yet examined. In a heavy mineral separation of this sandstone, the minerals cordierite; green, brown, and blue tourmaline; and minor amounts of staurolite, zircon, and kyanite were identified. It is concluded, from the mineral and chemical evidence, that Libyan Desert glass was derived from Nubian Sandstone. Whether there is any connection between the origin of Libyan Desert glass and the origin of the nearby impact structures is undetermined.

Terrestrial implication of layering, bubble shape and minerals along faults in tektite origin

Abstract Both detrital mineral grains and minerals which crystallized in situ were first found in tektites along faults in Muong Nong-type indochinites from Kan Luang Dong, Thailand. The detrital mineral grains have the optical properties of quartz and are within the size range of quartz abundant in local soil and rock. Such a correspondence in grain size strongly implies that the tektites from Kan Luang Dong are locally derived. Layered tektites are probably the result of the accumulation in puddles of melt from flash fusion of bare patches of soil and rock. The faulting took place while the melt was very hot and the evidence for this is: (1) perfect welding of the fault-fractures with detrital grains equally embedded in the glass on either side of the welds, (2) growth of minerals along the faults, and (3) warping of the fault planes by movement of the melt following faulting.

Micromorphology and Surface Characteristics of Lunar Dust and Breccia

Although nothing of direct biologic interest was observed in the sample studied, small shaped glass particles and glazed pits resemble objects which elsewhere have been described as fossils. These features, although nonbiological, do bear on processes of lunar weathering and outgassing. The glazed pits are impact features. Fusion of their surfaces released gases. Electron microscopy of the glasses, pits, and angular microfractured mineral grains indicates a prevalence of destructive weathering processes-thermal expansion and contraction, abrasion by by-passing particles, and, of course, impact. ous at room temperature.

Devitrification of glass around collapsed babbles in tektites

Abstract Devitrification was first observed around partly collapsed bubbles (vacuoles) in Santa Mesa philippinites heated by the fire which destroyed Manila near the end of World War II. This localization of devitrification furnishes independent evidence that bubbles in normal tektites were formed by water vapor and that the very low pressure in normal tektite bubbles resulted from the absorption in or reaction of the water vapor with the surrounding tektite glass. Although tektites are essentially anhydrous they do contain a trace of water, in fact more than enough to form all the bubbles found in tektites. Experiments show that a similar amount of devitrification and partial collapse of bubbles takes place in philippinites when heated about 4 days at a temperature of 825°C. Under identical conditions of time and temperature australites, indochinites and javanites showed equivalent amounts of change in shorter times. Bediasites showed no change in 7 days. Neither collapse nor devitrification took place around bubbles in Muong Nong-type tektites, indicating that water vapor was not an important constituent of the gas forming these bubbles and that the pressure in the bubbles approaches equilibrium with atmospheric pressure.

STRATIGRAPHY OF THE UPPER CAMBRIAN, LLANO UPLIFT, TEXAS

The two formations and eight members that constitute the Upper Cambrian in the Llano uplift of central Texas are described or redefined, and their lithic characters in 19 measured sections are graphically summarized. Standard reference to them is thus furnished. The Riley formation comprises the basal Paleozoic strata of the Llano uplift. Its initial sediments were deposited on a submerged pre-Cambrian terrane having a known topographic relief as great as 800 feet. Its thickness normally averages about 680 feet but ranges from probably less than 200 to about 800 feet. At most places it is subequally divisible between the Hickory sandstone member below and the Cap Mountain limestone member above, with the thin but widespread, glauconitic Lion Mountain sandstone member capping and completing the sequence. The Wilberns formation includes five named members between the Riley formation and rocks of the Lower Ordovician Ellenburger group. It normally averages about 580 feet thick and ranges from 540 to 610 feet thick, but in the southeastern corner of the Llano uplift truncation of the upper beds has reduced it to 360 feet. The thin but widespread, nonglauconitic Welge sandstone member introduces the sequence. Above it is the Morgan Creek limestone member, grading to the succeeding argillaceous beds of the Point Peak shale. At the top of the sequence are the San Saba limestone and Pedernales dolomite members. These two are essentially equivalent and gradational facies, with the Pedernales normally overlying the San Saba.

Rayed bubbles in tektites

Abstract The discovery of thin rays extending outward from bubbles in indochinites and a moldavite adds another link to the evidence that tektites formed very quickly at high temperatures from terrestrial rocks, and cooled rapidly. The rays have a refractive index between 1.49 and 1.51, which is in the range of refractive index of albitic glass. The rays may be the result of explosive volatilization of a hydrous sodium aluminum silicate.