0.55g part endcut. Forsterite chondrite !
Sold in a membrane box with label/certificate of authenticity
During the Munich Mineral Show in 2010, Fabien Kuntz bought a lot of chondrites from the Sahara. Among them, he noticed a meteorite that had an interesting look – outside, chondrules made him think of a type 3 chondrite.
When cutting, the heterogeneity of the color of chondrules was reminiscent of an H chondrite or a more strange chondrite. On the advice of the Planetary Studies Foundation (Illinois, USA), a sample was sent to the University of Washington in Seattle (A. Irving and S. Kuehner). The meteorite NWA 7135 has been classified as an ungrouped chondrite but is part of a small group of meteorites (3 known specimens, the chondrite inclusions in Cumberland Falls, Acfer 370 and therefore NWA 7135): Forsterite chondrites (F-Group). NWA 7135 contains relatively small chondrules, which are richer in magnesium (Fayalite: 4-6%) than ordinary chondrites.
Similarly, chondrules are embedded in a metal-rich matrix which constitutes about 30% of the meteorite, twice as much as in the ordinary chondrites, and in a similar rate to the CO chondrites. We also note the presence of sulphide-rich phases, with pyrrhotite, pentlandite, daubreelite, oldhamite and djerfisherite, and also schreibersite (iron sulfide). These sulfides are unknown in the ordinary chondrites but are sometimes observed in E chondrites (Enstatite chondrites), in the Winonaites, and in Aubrites with inclusions of unequilibrated forsterite as Cumberland Falls.
The class of forsterite chondrites was suggested in 1977 by Graham et al. to include four meteorites : Winona, Pontlyfini and Mount Morris (now classified as Winonaites) and Kakangari (classified as Kakangarite), and for certain inclusions in Cumberland Falls. In 1981, Neal and Lipschutz suggested that the parent bodies of these F-chondrites had many similarities with the parent body of enstatite chondrites and that it formed in the same area of the primitive solar system.
Northwest Africa 7135 (NWA 7135)
Purchased: 2010 Oct
Classification: Ungrouped chondrite
History: Purchased by Fabien Kuntz in October 2010 from a Moroccan dealer at the Munich Show.
Physical characteristics: Brown stone (51.3 g) lacking fusion crust and with evident light-colored, round chondrules.
Petrography: (A. Irving and S. Kuehner, UWS) Composed of separated, mostly spherical, relatively small chondrules (mean 0.69±0.53 mm, n=40) in a matrix (~30 vol.%) rich in altered kamacite. Some chondrules contain interstitial feldspathic glass. Minerals are olivine, zoned orthopyroxene, pigeonite, diopside, subcalcic augite, Cr-rich chromite, pyrrhotite, pentlandite, daubreelite, oldhamite, schreibersite and rare barite. The presence of highly reduced sulfides and phosphides suggest an atypical ordinary chondrite.
Geochemistry: Olivine, predominantly Fa4.8-6.3 (N = 15), with some more ferroan grains Fa19.8-19.9 (N = 2); orthopyroxene, Fs7.0-21.8Wo0.4-1.5 (N = 3); pigeonite, Fs17.3Wo6.9; subcalcic augite, Fs13.3-22.2Wo25.4-29.9 (N = 2). The mean olivine composition (Fa6) is much more magnesian than for H chondrites of similar subtype. Oxygen isotopes (K. Ziegler, UNM): analyses of acid-washed subsamples by laser fluorination gave, respectively, δ17O = 3.207, 3.649, 3.262, 3.379, 3.859; δ18O = 5.175, 6.072, 5.326, 5.333, 6.450; Δ17O = 0.475, 0.443, 0.450, 0.563, 0.453 (all per mil). Oxygen isotopes plot in a region above the TFL and at relatively high δ18O values.
Classification: Ungrouped chondrite, high metamorphic type 3 or type 4.
Specimens: 10.44 g including one polished thin section at PSF; main mass with Kuntz.