Sample No.: LEW86540

Location: Lewis Cliff

Weight (g): 21.1

Field No.: 4944

Dimensions (cm): 2.2 x 2.4 x 1.1

Meteorite Type: Finest Octahedrite

Macroscopic Description: Roy S. Clarke, Jr.

This aerodynamically shaped, tektite-like specimen is a slightly out-of-round (2.2 x 2.4 cm) disk (1.1 cm thick), with a small segment (2-3 mm) missing from its edge. Anterior and posterior surfaces intersect at a sharp edge which undulates slightly from a plane. Maximum thickness (1.1 cm) is approximately at the center of this plane. The two surfaces are smooth and have an almost uniform radii of curvature, the radius of the anterior surface being roughly 2 cm and that of the posterior surface roughly 5 cm.

Surfaces are predominately reddish-brown due to weathering, have small black patches of remnant fusion crust, and have iridescent coloring particularly near the edge. Fine streamers of fusion crust (~0.1 mm) radiate from the center of the anterior surface to the edge, with a very small accumulation of fusion crust at the edge. Indications of a very fine Widmanstätten pattern stand in relief in several patches of the posterior surface and can be seen with low magnification.

Polished Section Description: Roy S. Clarke. Jr.

A median slice perpendicular to the anterior and posterior surfaces provided 2 cm² for examination. The anterior surface edge is coated with terrestrial weathering products from 10 to 100 pm thick. Some remnant fusion crust, invaded with terrestrial oxides, remains. The same fusion crust/terrestrial oxide association extends along about 2/3 of the length of the posterior edge. Layered fusion crust has accumulated to 120 um thick at one intersection of anterior and posterior surfaces. Kamacite throughout the section has been heat-altered to α2. Kamacite lamellae range from 15 to 40 μm wide, their length being 10 to 100 times their width. Schreibersite within 800 μm of the anterior surface has survived heating in the form of quenched eutectic melts. Within 800 μm of the posterior surface schreibersites are either eutectic melts or are melted at their edges. Schreibersites are small, numerous, within kamacite lamellae or at lamellae junctions, and generally in the 50 to 100 μm size range. Martensitic plessite occupies perhaps 60% or more of the surface area, and its Ni content in the 18 to 19 weight percent range approximates the bulk Ni content. This specimen is a finest octahedrite, possibly belonging to chemical group IIID.