Sample Petrographic Description
Sample Number | LEW 87002 |
Newsletter | 11,2 |
Location | Lewis Cliff |
Field Number | 4418 |
Dimensions (cm) | 2.5 x 1.5 x 1.0 |
Weight (g) | 6.92 |
Original Classification | Eucrite |
Updated Classification | Howardite |
Mineral Composition (%Fa & %Fs) | |
Ferrosilite (mol%): 12-31 | |
Weathering | |
Ae | |
Fracturing | |
A | |
Macroscopic Description - René Martinez | |
This pebble is an achondrite with black, vitric fusion crust covering about 70% of its surface. It has an igneous texture overall, but appears crushed. Very light colored pyroxene and plagioclase are present. | |
Thin Section Description (,4) - Brian Mason | |
The section is made up of clasts, up to 1.2 cm across, of pyroxene with minor plagioclase, in a comminuted groundmass of these minerals. One clast, 6x3 nun, consists of an ophitic intergrowth of plagioclase and pyroxene. Pyroxene composition is Wo3Fs31; plagioclase composition averages An92 (Na2O 0.8-1.0%). The ophitic clast contains both orthopyroxene (Wo5Fs31) and augite (Wo44Fs12) with some intermediate compositions: plagioclase is An91. While the bulk composition approximates that of a howardite, this meteorite lacks the diogenetic pyroxene characteristic of the howardites; it is probably best classified as an Mg-rich eucrite. | |
Reclassification Notes (AMN 36,2) | |
LEW 87002, initially classified as a Eucrite, Mg-rich (Antarctic Meteorite Newsletter 11(2), page 29, 1988), is a fragmental breccia containing mm-sized clasts of low-Ca pyroxene, a mafic clast with subophitic texture, and a matrix composed mostly of low-Ca pyroxene and plagioclase. Low-Ca pyroxenes in the matrix, the margins of orthopyroxene clasts, and from the margin of the mafic clast are relatively uniform in Fe/Mg and have compositions of Wo2.5-3.5En64.4-66.3Fs31.0-32.1. High-Ca pyroxene compositions in the same petrologic settings are Wo40.4-42.0En43.4-45.4Fs14.3-15.3. The most magnesian orthopyroxene in the core of a mm-sized clast is Wo0.8En77.0Fs22.2, the most ferroan low-Ca and high-Ca pyroxenes from the mafic clast core are Wo2.5En58.1Fs39.4 and Wo43.0En41.2Fs15.8. Olivine compositions are Fo60.6, plagioclase compositions range from An94.6Ab5.2Or0.2 to An87.0Ab12.4Or0.6. The bulk rock composition determined by Warren et al. (2009; GCA 73:5918) has a subchondritic Eu/Sm and major element composition consistent with a mixture of diogenite:basaltic eucrite of ~65:35. LEW 87002 is a howardite exhibiting an exceptional degree of post-assembly metamorphism that caused large-scale Fe-Mg exchange. |
Antarctic Meteorite Images for Sample LEW 87002 | ||||
Lab Photo(s) : | ||||
Antarctic Meteorite Images for Sample LEW 87002 | ||||
Thin Section Photo(s) : | ||||
References for Sample LEW87002 | |
Mittlefehldt, D. W., Herrin, J. S., Quinn, J. E., Mertzman, S. A., Cartwright, J. A., Mertzman, K. R., Peng, Z. X., 2013, Composition and petrology of HED polymict breccias: The regolith of (4) Vesta. Meteoritics & Planetary Science, 48, 2105-2134, http://dx.doi.org/10.1111/maps.12182. | |
Warren, P. H., Kallemeyn, G. W., Huber, H., Ulff-Møller, F., Choe, W., 2009, Siderophile and other geochemical constraints on mixing relationships among HED-meteoritic breccias. Geochimica et Cosmochimica Acta, 73 Issue 19, 1-Oct-09, 5918-5943, ISSN 0016-7037, http://dx.doi.org/10.1016/j.gca.2009.06.030. |