CAI's

August, 2000

Lab Photo Homepage

Silicate-rich inclusions (SRI's)

in a "new"stony-iron meteorite

Analysis and description by:

Russell Kempton, New England Meteoritical Services

As reported in Meteoritics, Vol 16:361, 1981:

The Penwell Stony-iron Meteorite ......a distinctly new type of stony-iron meteorite was found near Penwell, Ector County, Texas USA in the Spring of 1981 (31°45'13"N. 102°29'33"W). This locality is near the Odessa Crater.

The Penwell meteorite has the texture of a mesosiderite. It contains approximately 50% iron-nickel, 30% silicates and 20% graphite by weight. These major phases are well separated from each other in relatively large grains. The graphite is well twinned and has a cliftonite structure when it is found in or near iron-nickel grains. The Kamacite contains 4.8% Ni. Other phases identified include taenite, shreibersite, olivine, orthopyroxene, augite plagioclase, and troilite. Penwell is distinctive with respect to its high graphite and low troilite contents.

The following year, in 1982, Penwell was revisited:

"....in the abstracts of the 44th Annual Meeting of the Meteoritical Society a new stony-iron meteorite found at Penwell near Odessa, Ector County, Texas, USA was reported. This meteorite was characterized by a high concentration of cliftonite graphite.

Additional study of this meteorite shows that the non-metallic phases are similar to those found in silicate inclusions of the Odessa iron meteorite....."

It thus appears that it is possible that the parent meteoroid of the Odessa iron contained various silicate inclusions which may have broken free during entry and been scattered over a moderately large area.

So, "Penwell" is Odessa - with a small difference. The silicate inclusions in Odessa are finer grained than "Penwell" indicating they experienced different cooling histories in the parent body.

By iron meteorite standards, the silicate inclusion in our photograph is huge measuring more than 4 cm in width. Microprobe analysis shows 5.1% Olivine, 11.4% plagioclase, and 6.6% orthopyroxene. Additionally, it is far more coarse grained than any inclusions that we have seen in Odessa.

This, to my knowledge, is the only published photograph of a "Penwell" SRI - enjoy!

Reference Sources:

Buchwald, V.F., "Handbook of Iron Meteorites, Their History, Distribution, Composition and Structure", Vol. 3, 1975

Kerridge, J., Matthews, M., "Meteorites and the Early Solar System", 1988

"Meteoritics" - Abstracts of Papers, 44th Annual Meeting of the Meteoritical Society, Vol. 16, Number 4, 361, 1981

"Meteoritics" - Vol. 17, Number 4, 256, 1982

Papike, J.J. "Planetary Materials", Reviews in Mineralogy, Volume 36, 1998