Romero H4

Earlier this year Arizona State University released about a hundred surplus thin sections. This was through a trade with meteorite dealer Anne Black. I bought a few of these slides from her. I chose the only Romero H4 she had because it had an inclusion.

The write up in the Meteoritical Bulletin Database gives only basic information on Romero so I searched further. I found a 1983 paper by Andrew L. Graham of the British Museum that actually addresses an inclusion in Romero. His Acknowledgement at the end of the paper was an even bigger surprise: “I thank Dr. C. B. Moore, Center for Meteorite Studies, Arizona State University, Tempe for the loan of the thin section of Romero (454.4X) containing the inclusion.” ASU! I checked my thin section and there, etched on the back, is ROMERO 454.4x. Mine might not be the same section since the paper cites microprobe data and my section is covered making such work impossible. Also, ASU’s Master list mentions two thin sections in its inventory. Still, the descriptions of Romero and the inclusion are a great fit.

Here I excerpt Dr. Graham’s paper to caption my photos:

I thank Dr. C.B. Moore, Center for Meteorite Studies, Arizona State University, Tempe for the loan of the thin section of Romero (454.4 x) containing the inclusion.

The Romero meteorite is an H3-4 chondrite which was found in Texas in 1938. It contains fairly abundant chondrules which are easily seen on a cut and polished surface. In thin section the general texture of the stone is that of chondrules and chondrule fragments set in a fine grained matrix. About 20% of the stone is composed of easily recognized rounded or sub-rounded chondrules . . .

Occasionally these chondrules are armoured by metal but generally the metal is homogeneously distributed within the matrix.

A clast in the Romero chondrite which is texturally and chemically distinct from both matrix and chondrules . . . The inclusion approximates to an ellipsoid in shape with a major axis of approximately 7 mm.

A metal-poor inclusion . . .

The boundary between the inclusion and the surrounding matrix is not always well defined but the textural distinction remains and the brown microcrystalline ‘glass’ differs obviously from the darker interstitial material present in the bulk of the meteorite.

The Variation in texture of the Romero inclusion is not random; one side has more ‘glass’ and more finely crystalline olivine than the other, which is similar to porphyritic olivine chondrules. This Variation suggests there was a cooling-rate gradient across the inclusion at the time of nucleation of the olivines and during the subsequent cooling.

There is no definite boundary between the various textures within the inclusion but there is a suggestion of layering which has been disturbed.

The inclusion is poorer in metal and sulphide than the rest of the meteorite and these phases, where they adjoin in the inclusion, are consistently inter-grown in a globular fashion, indicative of rapid cooling to below 900°C. This texture is rare in the bulk of the stone but it does occur.

Olivines set in a pale brown, microcrystalline and/or glassy matrix.

About the Author

John is a natural history enthusiast living in Oregon.

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