||Ungrouped Primitive Achondrite
||Found 2000, Tenre Desert, Nigeria
||2 double polished covered thin sections
Twenty-six pieces with a total weight of ~110 kg were found by Bernard Dejonghe on an
ancient alluvial plain. The two largest weigh ~30 kg each. Twenty stones were found on a trip in
early 2000, and six more in 2001 March. The geographic coordinates of these meteorites are
being withheld by the finder for three years. Classification (M. Bourot-Denise, MNHNP): Fa29.
3, pyroxene Fs24.3; ~30 vol% millimeter-sized relic chondrules are clearly visible in
backscattered electron images. Textures and relative abundances of the phases vary
considerably. The dominant lithology has a coarse grain size. It consists of olivine (poikilitically
enclosed within pyroxenes in the relic chondrules), a small amount of plagioclase, 10% metal
in rounded or oval-shaped grains often edged by chromite, and minor sulphides in small
grains. The interchondrule matrix consists of subhedral crystals of olivine embedded in
plagioclase and within anhedral crystals of chromite and phosphate that are up to 1 mm in
size. Two distinct plagioclase compositions are present: An46.4Or2.2 in the matrix and An26.
6Or5.2 in chondrule relics. A second lithology is finer grained and porous, without large metal
grains but with fairly abundant sulphide grains. The large metal grains are composed of
kamacite (6% Ni, 0.6% Co) and martensite (12% Ni, 0.4% Co). Some smaller metal grains
associated with sulphides are made up of taenite (up to 36% Ni, 0.2% Co) with martensite
cores. The sulphide is troilite (Cr 0.02–0.08%), with some grains containing inclusions of Cu-
bearing pentlandite. See also Bourot-Denise et al. (2002). Bulk chemistry (J. Zipfel and B.
Spettel, MPI; H. Palme, Köln): refractory lithophiles fractionated compared to a typical CR
composition, leading to possible classification as a primitive achondrite (Zipfel et al., 2002).
Oxygen isotopes (M. Javoy, IPGP): δ17O = +0.18 ± 0.08‰, δ18O = +2.94 ± 0.2‰.
Weathering grade, W0/1; shock stage, unknown. Specimens: type specimen, 396 g plus five
polished sections, MNHNP; main mass partly left in Niger, partly with the finder.
A 3.61 kg stone, labeled "Te-1", was found in 2000 March, probably on the same expedition
noted above, and is reported by J. Otto (Frei) to have been found in the Tenere Desert at 20°
45.8' N, 10°26.5' E. Classification (J. Otto and A. Ruh, Frei): a primitive achondrite; partly
covered with black fusion crust; shows a recrystallization texture with abundant 120° triple
junctions dominated by olivine (56 vol%, 100–700 µm, Fa28.7, 0.06 wt% CaO) and poikilitic
orthopyroxene (23 vol%, up to 3 mm, Fs25.4Wo3.6) with exsolved clinopyroxene (Fs12.
7Wo39.7); Fe-Ni metal is irregulary distributed (~10 vol%, up to 5 mm); poikilitic plagioclase
occurs in interstices (6.5 vol%, An38.5Or3.7); troilite (~3.5 vol%, 0.01 wt% Ni); chromite (~1
vol%, Fe/(Fe + Mg) = 0.817, Cr/(Cr + Al) = 0.818). Oxygen isotopes (R. Clayton and T.
Mayeda, UChi): δ17O = –0.85‰, δ18O = +1.70‰, different from other achondrites. Noble
gases (L. Schultz, MPI): data compatible with those of brachinites; exposure age is ~45 Ma.
Shock stage, S1/2; weathering grade, W0.