NWA 3152

EucriteMost common type of achondrite meteorite and a member of the HED group. Eucrites are basalts composed primarily of pigeonite and anorthite (An60-98). Eucrites have been placed into three subgroups based on mineralogical and chemical differences. • Non-cumulate eucrites represent the upper crust that solidified on a magma ocean after
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 crustMelted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of  4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below. 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 eucriteMost common type of achondrite meteorite and a member of the HED group. Eucrites are basalts composed primarily of pigeonite and anorthite (An60-98). Eucrites have been placed into three subgroups based on mineralogical and chemical differences. • Non-cumulate eucrites represent the upper crust that solidified on a magma ocean after of type 7.

As with martian and lunar basalts, eucritesMost common type of achondrite meteorite and a member of the HED group. Eucrites are basalts composed primarily of pigeonite and anorthite (An60-98). Eucrites have been placed into three subgroups based on mineralogical and chemical differences. • Non-cumulate eucrites represent the upper crust that solidified on a magma ocean after have experienced extensive igneous processing including melting. In a manner similar to that employed for the chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such groups, the eucrites have been petrologically divided into a metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. 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 basaltBasalt is the most common extrusive igneous rock on the terrestrial planets. For example, more than 90% of all volcanic rock on Earth is basalt. The term basalt is applied to most low viscosity dark silicate lavas, regardless of composition. Basalt is a mafic, extrusive and fine grained igneous rock studied; e.g., clasts in Y-75011, Y-75015, and Y-74450
2. Type 2—metastable Fe-rich pyroxenes are absent; mesostasisLast material to crystallize/solidify from a melt. Mesostasis can be found in both chondrules, in the matrix around chondrules, and in achondrites as interstitial fine-grained material such as plagioclase, and/or as glass between crystalline minerals.   glass is no longer clear; e.g., Pasamonte
3. Type 3—zoning from coreIn the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. to rim is less defined with an increase in Ca towards the rim; pyroxenes becoming cloudy; coarsening of pyroxenes resulting from augiteHigh-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, that occurs in many igneous rocks, particularly those of basaltic composition. In order to be considered augite, the clinopyroxene must contain 20 to 45 mol % of calcium (Wo20 - 45). An important and unique Martian meteorite is NWA 8159, that has been classified as an augite basalt. exsolutionSegregation, during cooling, of a homogeneous solid solution into two or more different solids. lamellae; e.g., clastA mineral or rock fragment embedded in another rock. 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 pigeoniteLow-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, found as a major mineral in eucrites and shergottites. In order to be considered pigeonite, the clinopyroxene must contain 5 to 20 mol % of calcium (Wo5 - 20). Chondrites of petrologic types 4 and below contain significant low-Ca clinopyroxene. During metamorphism to higher temperatures, all existing 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 orthopyroxeneOrthorhombic, low-Ca pyroxene common in chondrites. Its compositional range runs from all Mg-rich enstatite, MgSiO3 to Fe-rich ferrosilite, FeSiO3. These end-members form an almost complete solid solution where Mg2+ substitutes for Fe2+ up to about 90 mol. % and Ca substitutes no more than ~5 mol. % (higher Ca2+ contents occur 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 plagioclaseAlso referred to as the plagioclase feldspar series. Plagioclase is a common rock-forming series of feldspar minerals containing a continuous solid solution of calcium and sodium: (Na1-x,Cax)(Alx+1,Si1-x)Si2O8 where x = 0 to 1. The Ca-rich end-member is called anorthite (pure anorthite has formula: CaAl2Si2O8) and the Na-rich end-member is albite, along with accessory phases such as orthopyroxene, ilmeniteTi-Fe oxide, TiFeO3, found in achondrites, lunar mare basalts, and shergottites. Ilmenite forms as a primary mineral in mafic igneous rocks. It crystallizes relatively early out of a magma before most of the other minerals, and as a result, the heavier crystals of ilmenite precipitate to the bottom of the magma, Ti-chromite, and a silicaSilicon dioxide, SiO2. polymorph (Irving and Kuehner). The specimen of NWA 3152 shown above is a 1.21 g partial slice.