A Chondrule in the Chainpur Meteorite

An exceptionally large chondrule in the Parnallee meteorite

A giant chondrule, nearly 4 cm in diameter, has been found in the Parnallee meteorite, and is described, with analysis. An estimate of the composition of the partly devitrified groundmass falls within the known compositional range of chondrule glasses. The bulk composition of the chondrule is very close to the bulk composition of the meteorite excluding metal and sulphide.

The Barwell meteorite

Part of a meteorite was seen to fall on a road (52° 33′ 55″ N., 1° 20′ 23″ W.) in the village of Barwell, Leicestershire, at about 16.20 hrs G.M.T. on 24 December 1965. Fragments have been found over an area some ¾ mile long by ½ mile across, and appear to have been part of a single stone, of which 44 Kg (97 lb) have been recovered. The distribution, impact effects, and crustal morphology of the recovered fragments are described. Barwell is a moderately metamorphosed white olivine-hypersthene chondrite; a chemical analysis, with the derived Wahl norm, and a modal analysis are given, together with optical data and electron-probe analyses of the principal constituent minerals.

Chondrules: An Origin by Impacts between Dust Grains

A barred chondrule in the Ngawi meteorite contains a magnetite spherule embedded in it. The collision between these two objects fractured and partially remelted the chondrule, an indication that the impact velocity was 10(5) to 10(6) centimeters per second. This observation supports Cameron's and Whipple's recent predictions that grains achieved high velocities in the nebula and that the resulting impacts provide a suitable chondrule-forming mechanism.

Lunar Glasses and Micro-Breccias: Properties and Origin

Impact has been an important rock-forming process on the moon. Electron- and ion-probe analyses of major and minor elements show that most glasses and chondrule-like particles formed by shock melting of various proportions of mainly pyroxene, plagioclase, and ilmenite. This is the first direct evidence that chondrule-like molten droplets can form in impact events. Welding and shock lithification resulted in rocks texturally similar to chondrites but composition rules out the moon as source for chondrites. Impact craters on a nickel-iron sample evidence the importance of secondary impacts by accelerated lunar matter.

Xenon-Iodine Dating: Sharp Isochronism in Chondrites

Measurements of the accumulation of Xe(l29) from radioactive decay of extinct 1(129) in meteorites show that the 1(129)/ 1(127) ratio in high-temperature minerals in diverse chondrites was 10(-4) at the time of cooling. The uniformity in the ratio indicates that the minerals cooled simultaneously within 1 or 2 million years.

Chainpur-like Chondrites: Primitive Precursors of Ordinary Chondrites?

Chainpur and similar, apparently primitive, chondritic meteorites may be precursors of ordinary chondrites; a variety of evidence supports this working hypothesis. In general, carbonaceous chondrites seem to be related collaterally to this genetic sequence rather than being direct ancestors of ordinary chondrites. Metamorphic processes may be responsible for fractionations of elements such as indium and iodine, and type-II carbonaceous chondrites seem to be more primitive than types I or IIIA.