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NWA Eucrite (Unclassified)

Eucrite, monomict (tentative classification)
standby for northwest africa eucrite photo
Found 2006
coordinates not recorded

A single 16 g stone covered with a black fusion crust was found in the Sahara Desert and subsequently purchased by S. Turecki from Moroccan dealer A. Habibi. A type sample was submitted to Northern Arizona University (T. Bunch and J. Wittke) for analysis and classification but the provenance link has since been lost. It is presumed that this meteorite is a eucrite with a texture and mineralogy consistent with that of a monomict breccia.

The photo above shows a 2.1 g complete slice of this Northwest Africa eucrite. The top photo below shows the small fusion-crusted stone after initial sampling. The bottom photo is a different view of a complete slice from this eucrite.

standby for northwest africa eucrite photo

standby for northwest africa eucrite photo
Photos courtesy of Aziz Habibi


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NWA 3152

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

standby for northwest africa 3152 photo
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.


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NWA 999

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

standby for northwest africa 999 photo
purchased 2001
no coordinates recorded

Multiple stones and fragments totaling ~823 g were purchased in Morocco by an association of meteorite collectors known by the name of Trinity Meteorites. The exterior of this eucrite is covered with black fusion crust, and the interior is light tan in color with an ultra fine-grained texture, with mineral grains of pyroxene and plagioclase measuring tens of microns in size.

Northwest Africa 999 is a brecciated eucrite, possibly monomict, composed of very fine-grained basaltic material, which represent both the host and clasts in the meteorite. Widely scattered shock-melt veins of glass are present. The very fine-grained texture of this eucrite is consistent with rapid cooling from an extruded igneous melt. Although it exhibits the typical thermal metamorphic features characteristic of other equilibrated eucrites, it does not exhibit a high degree of textural equilibration (Warren and Choe, 2009). From a preliminary analysis performed by UCLA, NWA 999 was determined to be an extremely fine-grained eucrite that is slightly Fe-rich and REE-rich. The bulk composition of this eucrite plots with the Main Group–Nuevo Laredo trend. Black mineral grains (possibly chromite) are interspersed throughout the matrix, and a rare FeNi-metal grain is present in the specimen shown above. This eucrite experienced low- to moderate-shock and is cross-cut by thin, dark-gray, shock-melt veins. The specimen of NWA 999 shown above is a 2.44 g slice.


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Igdi

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

standby for igdi photo
Found February 2000
29° 14′ N., 8° 22′ W.

A 1,470 g meteorite was recovered in several pieces in Morocco. Igdi is composed of plagioclase, pigeonite with exsolved clinopyroxene, silica, ilmenite, chromite, and troilite. The Nuevo Laredo trend eucrites are thought to be the product of in situ crystallization of residual melts in a differentiating magma ocean. This origin is consistent with the decoupling between major elements and incompatible trace elements; i.e., for an increase in incompatible element abundances there is a decrease in Mg/(Mg + Fe). On a plot of Mg# versus an incompatible element such as Ti, Igdi falls comfortably within the Nuevo Laredo trend meteorites. The Nuevo Laredo trend has been combined with the Main Group eucrites in the currently recognized classification scheme (Barrat et al., 2007).

In a study of several Antarctic non-cumulate basaltic eucrites by Bermingham et al. (2008), a possible new subgroup was identified. In contrast to the other eucrites studied, members of this new subgroup exhibit LREE-depleted patterns with positive Eu anomalies, and other incompatible trace element abundances are lower than those in the other non-cumulate basaltic eucrites studied. Moreover, in contrast to the plagiophile elements in the other eucrites studied, the new subgroup contains higher Sr/Nd ratios when plotted against the magnitude of the Eu anomaly. It was proposed that this new subgroup might represent a parental source which was enriched in a plagioclase melt. It should be considered that high Sr, Ba, and Pb concentrations could be the result of severe weathering. The specimen of Igdi shown above is a 2.2 g complete slice.


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Dho 182

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

standby for dhofar 182 photo
Found February 9, 2000
18° 56′ 30′ N., 54° 30′ 5′ E.

Several conjoint fragments of this eucrite were found within a few meters of each other, weighing together 268 g. Dhofar 182 is a very recent fall with a weathering grade of W0, as attested by the shiny black fusion crust covering the fragments.

The photo shown above is a 0.28 g crusted fragment, while that below shows a 90.1 g fragment with fresh black fusion crust and a view of the light-colored interior.

standby for dhofar 182 photo
Photo courtesy of JNMC–Zurich