Kuehner1, D. Rumble, III2, R. L. Korotev3 and S. Clary. 1Dept. of

Earth & Space Sciences, University of Washington, Seattle, WA

98195, USA, irving@ess.; 2Geophysical Labora-

tory, Carnegie Institution, Washington, DC, 20015, USA; 3Dept.

of Earth & Planet. Sciences, Washington University, St. Louis,

MO 63130, USA.

Discovery: A single dark gray, flattened stone (698.8 g), ex-

hibiting subparallel contraction cracks and partially coated with

black, vesicular fusion crust was found in 2004 in the Moapa

Valley, southeast of Logandale, Nevada.

Petrography: Rounded to ellipsoidal objects (0.05 to 0.7 mm

across), exhibiting a preferred orientation of their long axes, are

set in a very fine grained, dark matrix containing small clusters

of sulfide grains.  The larger objects (presumably former chon-

drules) are composed mainly of serpentine minerals and S-

bearing phase(s) (probably tochinilite), and in thin section range

in color from pale yellow-brown to red- brown to sepia brown;

some such objects have serpentine-rich rims and/or larger, sub-

hedral, dark brown grains composed of serpentine/cronstedtite. 

The sulfides consist of finely intergrown pyrrhotite and pentland-

ite.  Very rare magnetite and calcite are present in the matrix, and

the specimen is traversed by narrow open fractures and several

thin veinlets filled with chalcedony. 

Broad electron beam analysis of different components gave

the following ranges in composition (in wt.%): ellipsoidal objects

SiO2 31.7-38.4, TiO2 0.07-0.25, Al2O3 1.8-7.2, Cr2O3 0.19-0.73,

FeO 15.9-26.3, MnO 0.07-0.18, MgO 22.7-28.8, CaO 0.06-0.25,

Na2O 0.04-0.29, SO3 0.03-0.87, SUM 85.7-87.4; matrix SiO2

27.1-28.4, TiO2 0.11-0.16, Al2O3 2.7, Cr2O3 0.48-0.57, FeO 34.1-

39.7, MnO 0.20-0.25, MgO 14.7-16.5, CaO 0.36-2.9, Na2O 0.21-

0.42, SO3 3.9-8.5, SUM 89.9-94.1.  The specimen must be very

porous on a fine scale, judging from the great difficulty in fully

degassing small fragments under vacuum.

Oxygen Isotopes: Analyses of two acid-washed whole rock

fragments by laser fluorination gave, respectively, δ18O = 6.29,

6.08; δ17O = 0.93, 0.68; Δ17O = -2.382, -2.519 per mil. These

compositions plot on the CM chondrite trend [1], close to com-

positions for anomalous CM2 chondrite NWA 3340 [2] and an-

other, 19 gram non-Antarctic CM1 chondrite from Northwest

Africa [3].

Bulk Composition: INAA of two ~100 mg samples gave the

following mean abundances: FeO 28.7 wt.%, Na2O 0.11 wt.%,

Ni 1.6 wt.%; in ppm, Sc 8.9, Cr 3900, La 0.38, Sm 0.24, Eu 0.06,

Yb 0.28, Lu 0.041.  The REE pattern is flat at ~1.3xCI chon-

drites, and is similar to those of other CM chondrites [4]. 

References: [1] Clayton R. N. and Mayeda T. K. 1999. Geo-

chim. Cosmochim. Acta 63:2089-2104. [2] Kuehner S. M. et al.

2007. Meteoritics & Planetary Science 32:A74. [3] Weisberg M.

K. et al. 2009. Meteorit. Bull. 96. [4] Wasson J. T. and Kalle-

meyn G. W. 1988. Phil. Trans. Roy. Soc. Lond. A325: 535-544.

Over the years NevadaMeteorites has been working to provide new material and strewn field data for scientific study. Some of the more significant meteorites include two rare finds in the United States. Blue Eagle well an R3-6 Rumurti chondrite and Moapa Valley a CM1 carbonaceous chondrite. Moapa Valley is being analyzed at the University of California Berkeley Space Sciences Laboratory for cosmogenic isotopes to estimate the cosmic ray exposure (or space) age of the meteoroid.  CM chondrites all have fairly short CRE ages in the range 100,000 to 2 million years.  Results are expected by early 2010. Another sample of Moapa Valley is being measured at the University of Arizona Accelerator Mass Spectrometry Laboratory for its content of carbon-14, which is produced mainly from oxygen atoms while a meteoroid is in space exposed to penetrating cosmic rays.  After a meteoroid lands (and becomes a meteorite) and is shielded from cosmic rays by our atmosphere, carbon-14 decays away slowly to nitrogen-14, and the amount remaining gives an estimate of the terrestrial (landing) age.  Because the half-life of carbon-14 is only 5730 years, this technique cannot be used for meteorites that fell over 70,000 years ago, but it is likely that Moapa Valley has a younger terrestrial age than that (perhaps 5,000 to 10,000 years).  Results are expected within 3 months. 

*  Cosmic Ray exposure or (space age) of Moapa Valley is 0.18 + / - 0.03 million years.

* Carbon -14 Dating 2000  +/- 1300 years.



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Sonny Clary Collection

Nevadameteorites has donated 31 lbs

of meteorite fragments, found in the

Nevada desert to TCU’s Oscar E. Monnig Meteorite Gallery to be used for educational outreach.

   Wisconsin Meteorite April 14 ,2010

              photo credit  Arlene Schlazer