The Boxhole meteorite crater has been described previously. It is in Central Australia at latitude 22° 37′ 30´″ S., longitude 135° 11′ 59″ E. During the single afternoon that was spent examining this great crater, nearly 200 yards across, most of the time was occupied with taking measurements and photographs, and only a few shale-balls were found in the way of meteoritic material. Mr. Joe Webb, who lives nearby, was instructed to continue the search, and in due course he sent down to Adelaide three pieces of iron weighing respectively 17 lb. 9 oz., 1 lb. 8 oz., and 5 oz., shown in figs. 1 and 3, together with six more shale-balls. This material was purchased by the South Australian Museum. Two other small pieces of iron have been obtained by the author from other sources.

A number of specimens of core-like australites possess well-developed flaked equatorial zones (text-fig. 1), on which peculiar grooves and flutings are present. These markings are here referred to as ‘bubble tracks’, the term indicating their apparent mode of formation. The specimens displaying these features are round and elongate forms. The round forms vary in diameter from 34 to 41 mm., the elongate forms range in length from 30 to 75 mm., while the weights vary from 27½ to 96 grams. Australites of these sizes are of infrequent occurrence, only twenty-one having been previously recorded (9, pl. 4), (2, pl. 4), and (3, pl. 9); the illustrations of these examples show that they have comparable features, such as flaked equatorial zones and bubble tracks.

Bavenite was first described from Baveno by Artini in 1901 as monoclinic crystals of prismatic habit in pegmatitic druses in granite and given the formula 3CaO.Al2O3.6SiO2.H2O. More recently, the mineral has been described pseudomorphous after beryl from Himalaya mine, Mesa Grande, San Diego County, California, by Schaller and Fairchild (1932) and shown to contain beryllium as an essential constituent. In 1933 X-ray determinations by Ksanda and Merwin indicated a unit cell with dimensions a 9·67, b 11·53, c 4·95Å, and showed the symmetry to be orthorhombic and referable to the space-group V1, Vh1, or C2v1. Revised crystallographic orientation and optical constants were also suggested by these authors.

The material about to be described is from two localities in Switzerland. Of fourteen specimens from a fissure in the rocks below the Muotta Nera, Piz del Laiblau, Val Nalps, Tavetschthal, Graubünden, selected by Mr. F. N. Ashcroft in 1935 and 1936 from a fairly large series stocked by Adolf Caveng of Sedrun, one (B.M. 1937,598) carries the mineral as roughly radiating aggregates of platy fibres of very pale brown colour in bulk.

The structure of sanidine was described by Taylor in 1933, and Taylor, Darbyshire, and Strunz in 1934 extended the investigation to include the potassium-barium-felspars and albite, and presented a small amount of experimental data for potash-soda perthitic felspars and for members of the plagioclase series. X-ray work on the potash-soda perthitic felspars has recently been reported by Ito and Inuzuka, by Ito, and by workers in this laboratory, and a preliminary report of an examination of the plagioclase felspars is given in a thesis presented by one of us (S.H.C.) in 1939 for the degree of Ph.D. in the University of Manchester.

The investigations to be described in this paper, as well as those already published from this laboratory, form part of a programme of researches dealing with various aspects of the problem of felspar structure, undertaken in an attempt to obtain a correlation between the physical and chemical properties on the one hand and the details of the structure on the other.