Newsletter |
9,2 |
Location |
Allan Hills |
Field Number |
2042 |
Dimensions (cm) |
2.0 x 1.8 x 1.0 |
Weight (g) |
2.80 |
Original Classification |
C2 Chondrite |
Updated Classification |
CM2 Chondrite |
Pairing |
ALH 82100;
ALH 82131;
ALH 84036;
ALH 84039;
ALH 84046;
ALH 84050;
ALH 84053;
ALH 90407;
ALH 99500;
|
Fayalite (mol%): 0.7-40;Ferrosilite (mol%): 2-13 |
A |
A |
Some of these specimens have pitted and fractured fusion crust while some have no fusion crust remaining. The interior of all of these is black with numerous clasts/chondrules that are <0.5 mm in longest dimension. Oxidation is present but minimal. Evaporite deposit has formed on ALH84050 and 054. |
Thin sections of all these C2 chondrites are so similar that they can be described as a group, and the possibility of pairing should be considered. ALH84033 (Antarctic Meteorite Newsletter 8(2)) is also similar. Olivine-rich chondrules up to 2 mm diameter, chondrule fragments, and irregular olivine-rich inclusions up to 1.5 mm across are present in a black to translucent brown matrix with many small mineral grains. Most of the olivine is near forsterite in composition, but occasional iron-rich grains (up to Fa40) were analysed. Pyroxene is not common, and is poly-synthetically-twinned clionoenstatite. Refractory inclusions up to 0.15-0.2 mm in size, and containing spinel + perovskite + hibonite, are common. Blue pleochroic hibonite is present in only a few inclusions in 036, 039, 046, and 054. |
Many carbonaceous chondrites were initially classified as C2 in early newsletters. These are mostly CM2, based on matrix properties, chondrules abundance and sizes, and therefore all these samples have been reclassified more specifically here as CM2. |
ALH 82100, ALH 82131, and ALH 84036, ALH 84039, ALH 84046, ALH 84050, ALH 84053, ALH 90407, and ALH 99500 are all from the far western icefield; although they have been paired for many years with ALH 81002, the latter is nearly 80 km away and too far to be reasonably paired given the ice flow regimes in that region. Additionally, available observations suggest ALH 99500 was erroneously paired with ALH 83100 - instead we suggest pairing with ALH 82100. AMN 45 no. 2. |