Other
Scientific paper
Mar 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996lpi....27..821m&link_type=abstract
Lunar and Planetary Science, volume 27, page 821
Other
Fractionation: Nickel, Meteorites: Iva Iron, Phosphide: New, Spheroids: Drusy, Vugs
Scientific paper
A 22.28-kg mass of iron, found in Albion, Washington, in the winter of 1966-1967 remained unknown until 1991 when the finder brought it to Carleton B. Moore at Arizona State University. Moore identified it as a meteorite and sent a sample to John A. Wasson at UCLA who classified it as a IVA fine octahedrite. This iron is unique in having vugs, ranging in length from 4 to 9 mm, scattered throughout the otherwise orderly Widmanstatten structure. Drusy spheroids cover the walls and partially fill some of the vugs. We have analyzed the constituents of one vug (Vug-A) and the metals surrounding it. The drusy spheroids consist mainly of small, irregular grains of kamacite containing 2-3.5 wt.% Ni and several rounded masses of tetrataenite (55.6 wt.% Ni). Both metals are enmeshed in troilite which appears to have invaded and corroded them. Daubreelite (FeCr2S4) in euhedral grains is scattered through the spheroids and elsewhere in the iron. It formed earlier than the troilite which contains no chromium and shows no sign of reaction where the two are in contact. A phosphide mineral in euhedral to subhedral grains, 3-15 um across, also occurs in the spheroids. Our analyses of sixteen grains yielded a consistent composition of [Ni 0.54 (Fe 0.46)3.7 P], which we are examining as a new species. The spheroids are rimmed with kamacite and show clear evidence of having grown in stages during the passage of a fluid or vapor phase. We regard the vugs as primary features inherited from bubbles in the cooling melt that remained open during formation of the Widmanstatten structures. Previous investigators have attributed masses of troilite-kamacite intergrowths to shock-melting of troilite nodules. However, we find it difficult to envision shock processes opening cavities, lining them with drusy minerals, and giving rise to a new phosphide without damaging the metal in which we find no evidence of shock effects. We are investigating further our hypothesis that the unique vugs in the Albion iron are of primary origin.
Kempton R.
Marvin Ursula B.
Petaev Michael I.
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