NWA 3152

Eucrite
Monomict, noncumulate
(Main Group–Nuevo Laredo trend)

purchased April 2005
no coordinates recorded

A relatively fresh (W1), tan-colored, 1,496 g stone that was partially covered by fusion crust was found in Northwest Africa and was subsequently sold to G. Hupé in Tagounite, Morocco. A sample was analyzed at the University of Washington in Seattle (A. Irving and S. Kuehner) and NWA 3152 was determined to be a highly metamorphosed basaltic eucrite of type 7.

As with martian and lunar basalts, eucrites have experienced extensive igneous processing including melting. In a manner similar to that employed for the chondrite groups, the eucrites have been petrologically divided into a metamorphic sequence comprising seven types (after Takeda and Graham, 1991; Yamaguchi et al., 1996):

1. Type 1—most rapidly cooled within the sequence; mesostasis-rich with a glass phase and original chemistry preserved; exhibits pronounced Mg–Fe zoning in pyroxenes; represents the least altered basalt studied; e.g., clasts in Y-75011, Y-75015, and Y-74450
2. Type 2—metastable Fe-rich pyroxenes are absent; mesostasis glass is no longer clear; e.g., Pasamonte
3. Type 3—zoning from core to rim is less defined with an increase in Ca towards the rim; pyroxenes becoming cloudy; coarsening of pyroxenes resulting from augite exsolution lamellae; e.g., clast in Y-790266
4. Type 4—only remnants of zoning still visible; cloudy pyroxenes present; mesostasis glass is recrystallized or absent; augite exsolution lamellae becoming resolvable in microprobe; e.g., Stannern, Nuevo Laredo
5. Type 5—homogenous host composition with readily resolvable exsolved pigeonite lamellae; pigeonites extensively clouded by reheating; mesostasis glass recrystallized or absent; e.g., Juvinas, Sioux Co., Lakangaon
6. Type 6—most slowly cooled eucrites in the sequence; the clinopyroxene pigeonite is partly inverted to orthopyroxene through slow cooling processes; pyroxenes contain Mg-rich cores and coarse augite exsolution lamellae; original mesostasis is absent; Ca is enriched in the rims; often have a brecciated texture; e.g., Millbillillie, Y-791186
7. Type 7—recognized as the most metamorphosed in the sequence (Yamaguchi et al., 1996); e.g., Palo Blanco Creek, Jonzac, Haraiya, A-87272, NWA 3152

Northwest Africa 3152 has a very fine-grained texture with exsolved pigeonite and plagioclase, along with accessory phases such as orthopyroxene, ilmenite, Ti-chromite, and a silica polymorph (Irving and Kuehner). The specimen of NWA 3152 shown above is a 1.21 g partial slice.