Nevada Meteorite Picture of the Day
(for the Month of May 2008)

Explanation:

The above image depicts a 1-inch-round thin-section of a Nevada meteorite as it rests on the stage (under the eyepiece) of my microscope. If you mouse-click on the above image, you will be linked to a close-up depiction of this thin-section. This thin-section is from the type specimen of a small meteorite fragment that was found very near the same locality as the specimen that is depicted in last month's NevMet POD. The lighting is not polarized; it is just reflected artificial light. The above view shows this light reflecting off some of the polished metal grains. The "close-up" depicts a lithological fabric of metal grains, troilite, and other opaque minerals, as wellas, chondrules that are equilibrated with the crystalline groundmass. All of which is typical for an ordinary chondrite. Typical, EXCEPT, for the fusion-crust (which is the black, vesiculated portion along the edges of this specimen). This fusion-crust is a little fresher (and thicker) than is typical for most meteorite "finds". The fusion-crust is actually two-toned in its black color. If you look closely, you'll see that the outer portion is a grayer shade than the charcoal black inner portion of the fusion-crust. This suggests that the fusion-crust is still in the process of devitrifying (chemical-weathering) and is out-pacing the mechanical-weathering of this rind. But for classification purposes, the degree of oxidation of the metal-grains (and not the condition of the fusion crust) is how the weathering grade is determined for meteorites this fresh. Speaking of classification, this thin section has been submitted to UCLA for classification. Should this specimen turn out to be "unpaired" to the other finds from this locality, this web page will be updated.

Many other meteorites were found at this same locality. The vast majority of these "other meteorites" were small fragments of an H6 meteorite fall. All of these small fragments have similar-looking exteriors. But after cutting some of these fragments and examining the interiors, it was obvious that they were not from the H6 meteorite. So, now that it is known that other meteorite types can be found from this locality, finders of future fragments now know not to assume that their find is from the H6 meteorite fall. So, the next time that the wisdom of classifying small specimens gets questioned, it should be kept in mind that the above piece of crucial information was obtained only through the classification of a small fragment.

For Reference:

If you have found a new Nevada meteorite and would like to report it 
and get a "provisional" name, or even easier, you have made a find 
from a known, formally named locality and would like to have a 
provisional number issued, 
please contact the Editor of the Meteoritical Bulletin, Dr. Michael K. Weisberg

Would you like to see your image displayed here? Feel free to submit your image to the editor's email address below. Any and all submissions of Nevada meteorite images are welcome.