MUSEUM OF NATURE The Agpalilik meteorite

Press, Volume CXV, Issue 33816, 12 April 1975, Page 11

MUSEUM OF NATURE The Agpalilik meteorite

I Contributed by the Canterbury Museum)

An interesting addition to the Canterbury Museum’s geological collection is a slice of the 20-tdn Agpalilik iron meteorite from north-west Greenland. This specimen was received from Dr V. F. Buchwald. in the Institute of Metallurgy, Lyngby, Denmark. in exchange for a slice of New Zealand's Waingafomia meteorite.

Although discovered only in 1963, the Agpalilik iron is part of the Cape York meteorite shower which 1 probably fell on to thick ice sometime during the last glaciation.

When Peary visited this region in 1894 he was shown three partly buried masses of iron by the local Eskimos. These had become familiar landmarks to the Eskimos who had called the largest Ahnighito, or bent,, an allusion to its shape and size, and the smaller fragments Woman (3 tons) and Dog (less than one ton).

Recognising these masses as meteorites, Peary brought them to New York in 1897. Today the Ahnighito meteorite (31 tons) is known to be the second largest in the world. Moraine cover Since 1894 several small fragments of the same shower have been found, the largest of these being the Agpalilik iron. This was found almost covered by glacial moraine and lying in silt and gravel that was frozen for most of the year. Surprisingly enough the exposed surface was less corroded than the buried faces which had been attacked during the brief Arctic summer by ground waters containing chlorides.

The Agpalilik meteorite was the first iron meteorite of any great size to be sectioned by a mason’s wire saw. Before 1967 large iron meteorites had been sliced by sawing between small closely spread holes drilled into its mass. This was far from satisfactory.

An entirely new mineral, chromium nitride, or Carlsbergite, was found dispersed throughout the Agpalilik meteorite. Sectioning also confirmed that at one time this meteorite was part of a giant crystal of Austentite. a high temperature mineral that re-crystallised, as the temperature dropped, to regularly spaced intergrowths of nickel iron alloys. In addition, the met-

eorite contained elongated inclusions of the cosmic mineral troilite, an iron sulphide, as shown in the photograph.

The troilite was found to be associated with chromite and phosphate minerals at. one end only of the inclusions. Dr Buchwald considers that metallic solidification advanced as a front through the mass so that the iron sulphide residue accumulated in elongated pockets; and the restriction of the chromite and phosphate minerals to one end of these pockets, indicates that crystallisa-

tion took place within a strong gravitational field. Most people are aware that meteoritic material is thought to have come from a fragmented planet, most of which is probably orbiting-the Sun between Mars and Jupiter.

Scientists have drawn conclusions about the composition of different layers within the Earth by studying the different type of meteorites that reach its surface from outer space. The iron meteorites are thought to have come from the core region of a planet. — M.A.B.