EETA79001 Petrographic Description

Antarctic Meteorite Newsletter, Volume 3, Number 3
August 1980

Sample No.:	EETA79001
Field No.:	1043
Weight (gms):	7942.0
Meteorite Type:	Shergottite
Location:	Elephant Moraine

Physical Description: Roberta Score
All but one surface of this achondrite (22 x 17 x 14 cm.) is covered with black fusion crust, but there are areas on all surfaces where the fusion crust has been plucked away. One surface has a deep regmaglypt that is covered with fusion crust. The areas devoid of fusion crust are white-gray in color and the matrix appears porous. Veins (~0.5 mm wide) of dark material criss-cross each other. Whitish-yellow clasts (Grimm diameter) are scattered all over this achondrite. Most of the specimen appears very fine-grained but a small part near the E surface has a different lithology.

Sawing this meteorite exposed a light colored interior with rounded white clasts, as large as 0.5 cm in diameter. Several large black fine-grained clasts as large as 2.5 cm are scattered over the cut face. Some of these black clasts contain glass lined vugs. Upon chipping one of these clasts containing a vug, the entire clast popped out easily with no matrix adhering to the clast. Numerous veins of black material criss-cross each other. Most of these veins run through a black clast. The longest vein is 14 cm long. Near the W end of the cut face are brownish colored clasts which may or may not be pyroxene. Ninety per cent of the cut face is fine-grained. Ten per cent (near the E end) of the cut face consists of intergrown pyroxene and feldspar in a basaltic texture.

Petrographic Description: Arch Reid
Thin sections were cut from the three different lithologies: 1) the main mass of the meteorite; 2) the material with basaltic texture that is present at one end of the sample, and; 3) the dark clasts included in the main mass.

The main mass is a shocked but unbrecciated pyroxenite with pyroxene as the major phase but also containing maskelynite, Mg-Al chromite, iron sulphide and ilmenite(?). The major pyroxene is polysynthetically twinned pigeonite (?) (resembling twinned clinobronzite) ranging in composition from Wo₅En₇₀Fs₂₅ to Wo₁₂En₅₀Fs₃₈. Orthopyroxene forms the cores of larger pyroxene grains and ranges in composition from Wo_1.5En₈₃Fs₁₆ to Wo₃En₇₈Fs₁₉,. The larger pyroxene grains, up to 3.5 mm, comprise untwinned cores zoned outward to polysynthetically twinned rims. The smaller pyroxenes, .3 to 1 mm, are twinned clinopyroxenes and are intergrown with maskelynite laths. The maskelynite ranges in composition from Or₁Ab₃₉An₆₀ to Or_1.5Ab₄₄An₅₅. A few large olivines, Fo₇₇ to Fo₇₃ range up to 2.5 mm.

The less abundant lithology closely resembles Shergotty in texture but is finer grained. The major minerals are clinopyroxene and maskelynite: calcium phosphate, SiO₂, ilmenite (?) and magnetite (?) are also present. Elongate clinopyroxene and laths of maskelynite are about one mm long and generally subparallel: many of the maskelynite grains contain pyroxene inclusions. Analyzed pigeonites range from Wo₁₀En₅₂Fs₃₈ to Wo₁₈En₁₅Fs₆₇. The maskelynite also shows a range in composition from Or_.5Ab₃₈An₆₂ to Or₄Ab₅₀An₄₆.

The dark clasts are apparently loci of melting; in many cases they connect with the thin black glassy (?) veinlets that traverse much of the meteorite. Thin sections from these dark areas show glass (with relict olivine, pyroxene and maskelynite inclusions), devitrified glass, areas with mosaic texture and vesicular areas with quench textures. The dark areas appear to be more common in olivine-bearing portions of the main mass.