Sample No.: ALH84165

Location: Allan Hills

Weight (g): 94.7

Field No.: 2198

Dimensions (cm): 4.3 x 3.3 x 1.5

Meteorite Type: Octahedrite

Macroscopic Description: Roy S. Clarke, Jr.

This ablation-shaped individual is essentially oval in outline when viewed along its axis of oriented flight through the atmosphere. Over most of its area the anterior surface has a fairly uniform radius of curvature that is greater than the radius of curvature of the posterior surface. The anterior radius of curvature, however, does decrease markedly toward the edge, and the anterior surface extends beyond the joint of the two surfaces. The result is a 1 mm ablation lip or flange, reminiscent of a flanged australite. Both surfaces are covered with reddish brown secondary oxides, the anterior surface being smoother than the posterior. Delicate streamers of fusion crust remain, however, along the anterior surface edge. They record flow of melt away from the stagnation point and parallel to the direction of orientation during flight. A fine crack 1.5 cm long is present on the anterior surface.

Polished Section Description,: Roy S. Clarke, Jr.

A median section perpendicular to a flat projection of the anterior surface, and approximately parallel to and including the axis of orientation, provided an area of 3 sq. cm for examination. The anterior edge is free of fusion crust, but a structure in kamacite penetrates 1.5 to 2 mm. The posterior edge has a continuous fusion crust accumulation 0.2 to 0.3 mm thick. The kamacite along this edge has also been penetrated to a depth of 1.5 to 2 mm by α2 structure. At the flanges, fusion crust accumulation is as thick as 1.5 mm. Taenite lamellae, taenite-plessite areas, and cellular plessite areas are present. The few opportunities for band width measurements suggest a tentative value of about 1 mm. Grain boundary schreibersite is present as is schreibersite associated with taenite. Kamacite is mottled and contains a pronounced ε-structure and occasional remnant Neumann bands.

This ablation-shaped and shock-affected octahedrite may prove to be a Group III meteorite.