CM Carbonaceous Chondrites

Cimarron (37.85° N, 100.35° W)

Gray County, Kansas USA
Found ~1948
Carbonaceous chondrite (CM2)

A single stone of unknown weight was found by a rancher on a farm 3.4 miles north of Cimarron and sent to the University of Kansas in the early 1950s. A piece was later acquired by a meteorite collector and samples given to NAU in 1998 and pieces to AMNH in 1992 and 1993. Classification and mineralogy (M Zolensky, JSC; and T. Bunch, NAU): olivine ranges from Fa1 to Fa64, with a peak at Fa1-2, average Fa1.2, PMD 11%. Low Ca-pyroxene ranges from Fs2Wo5 to Fs5Wo4, also present are diopside, enstatite-diopside, pigeonite, and chromite. Porphyritic olivine, barred olivine and granular olivine crystals are most abundant, maximum chondrule diameter is 2 mm. Chondrules are sparse, matrix and chondrule rims comprise ~85 vol. % of the meteorite. The percentage of matrix is similar to that of Bells and Nogoya, but the composition of these is lower in S and Mg, and higher in Si; this could be due to terrestrial weathering. Specimens: type specimen 21 g AMNH; 7.1 g, NAU.

Northwest Africa 3340

Algeria or Morocco
Find: April 2006
Carbonaceous chondrite (CM2, anomalous)

History: Purchased by F. Kuntz in April 2006 in Erfoud, Morocco, and subsequently acquired for the DuPont Collection at PSF.
Physical characteristics: Two pieces from a very fresh, broken, black, porous stone (total weight 12.7 g) with shiny fusion crust on one side.
Petrography: (A. Irving and S. Kuehner, UWS; T. Bunch, NAU) Sparse mineral grains, carbon-rich objects, dust-armored chondrules and rare refractory inclusion occur in a heterogeneous, very fine grained, porous matrix composed mainly of bladed phyllosilicates with some pentlandite and calcite (clearly visible under incident UV light). Olivine grains (up to 2 mm across) are commonly armored by fine, polycrystalline "dust" and contain inclusions of Ni-rich troilite, chromite, millerite, kamacite and taenite. Both pentlandite and magnesian olivine occur as separate smaller, angular grains. The carbon-rich objects (up to 50 m across) consist of either pure graphite or a chlorine-rich organic phase. Chondrules consist of PO and POP olivine, many having a fine-grained polycrystalline "dust" rims. One small refractory inclusion is composed of Mg-Al spinel with inclusions of perovskite.
Mineral compositions and geochemistry: Larger zoned olivine grains (e.g., Fa17.9-33.9, Fa39.966); smaller homogeneous olivine grains (e.g. Fa1.5, Fa19.9); pentlandite (Ni = 26.2 wt. %). Matrix phyllosilicate material could not be analyzed quantitatively, but has very consistent proportions of Mg, Fe, Si and S. The chlorine-rich organic phase contains ~17 wt.% Cl and ~32 wt. % C, but no detectable N and minor O. Oxygen isotopes: (D. Rumble, CIW) Replicate analyses by laser fluorination gave, respectively, δ18O = 0.494, 1.166; δ17O = 6.224, 7.049; Δ17O = -2.780, -2.542 (all ‰).
Classification: Carbonaceous chondrite (CM2, anomalous); minimal weathering. The presence of chlorine-rich carbon compounds, which may be enigmatic chlorinated hydrocarbons, makes this specimen potentially unique among CM chondrites.
Specimens: A total of 2.7 g of sample is on deposit at UWS and the remainder of the mass (10 g) is at PSF.