(C3-ung in MetBull 86)
no coordinates recorded A single stone weighing 98 g was purchased by B. Fectay in Tagounite, Morocco in 2000. Initial analysis and classification was conducted at Northern Arizona University (T. Bunch and J. Wittke), and NWA 1152 (syn. Tagounite 084) was determined to be a member of the CV3 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 Click on Term to Read More group. Subsequent analyses were conducted at the Natural History Museum, UK, while isotopic analyses were completed at The Open University, UK.
Northwest Africa 1152 is primarily composed of highly magnesian type-I PO and POP chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
(52.2 vol%) having average diameters of 0.9 mm (Smith et al.
, 2004). It exhibits features consistent with a shock stageA petrographic assessment, using features observed in minerals grains, of the degree to which a meteorite has undergone shock metamorphism. The highest stage observed in 25% of the indicator grains is used to determine the stage. Also called "shock level". Click on Term to Read More
of S2, and has experienced moderate to heavy oxidationOxidation and reduction together are called redox (reduction and oxidation) and generally characterized by the transfer of electrons between chemical species, like molecules, atoms or ions, where one species undergoes oxidation, a loss of electrons, while another species undergoes reduction, a gain of electrons. This transfer of electrons between reactants Click on Term to Read More
during its terrestrial residence, resulting in a weathering grade of W2 (W2/3 in MetBull 86). The meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More
has a relatively high matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More
content constituting 42.8 vol% and includes minor FeNi-metal phases (0.7 vol%) and rare refractory phases (0.3 vol%) comprising mostly AOAs and spinel-pyroxene aggregates.
Although initially classified as a CV3 chondrite, subsequent studies of NWA 1152 by Smith et al.
(2004) found that it has mineralogical and petrographic features that are wide-ranging, exhibiting similarities to both CR and CV chondritesMeteorite class named after the Vigarano meteorite that fell in Italy in 1910. They have abundant large, well-defined rimless (?) chondrules of magnesium-rich olivine (~0.7 mm diameter; 40-65 vol. %), often surrounded by iron sulfide. They also contain 7-20 vol. % CAIs. The often dark-gray matrix is dominated by Fe-rich Click on Term to Read More
. Perhaps of great significance is the fact that O-isotopic values plot within the CV field. They also found that NWA 1152 is similar in many characteristics to those of the ungroupedModifying term used to describe meteorites that are mineralogically and/or chemically unique and defy classification into the group or sub-group they most closely resemble. Some examples include Ungrouped Achondrite (achondrite-ung), Ungrouped Chondrite (chondrite-ung), Ungrouped Iron (iron-ung), and Ungrouped Carbonaceous (C-ung). Click on Term to Read More
C3 chondrite Sahara 00182. In a like manner, it has been demonstrated through compositional, isotopic, and petrographic data by Choe et al.
(2010) that Sahara 00182 is closely related (either genetically through parent bodyThe body from which a meteorite or meteoroid was derived prior to its ejection. Some parent bodies were destroyed early in the formation of our Solar System, while others like the asteroid 4-Vesta and Mars are still observable today. Click on Term to Read More
origin, or through petrological processes on similar chondritic precursor asteroids) to the C4 chondrite HaH 073, a meteorite previously associated isotopically and mineralogically by Weckwerth and Weber (1998) with the Coolidge/Loongana 001 carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than Click on Term to Read More
grouplet. In consideration of the complex variability that exists among these meteorites, and in spite of the fact that they reflect trends most similar to the CV and CR groups, Smith et al.
(2004) concluded that it was most reasonable to classify NWA 1152 (and Sahara 00182) as an ungrouped C3 chondrite. Subsequent in-depth studies of NWA 1152 (and other unusual C chondritesChondrites 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 Click on Term to Read More
) were carried out by Choe et al.
(2010). Despite clear differences in comparison to CV chondrites, and the close similarities when compared to CR chondrites, they concluded that NWA 1152 is most likely an anomalous member of the CV group.
Petrographic studies along with O- and Al/Mg-isotopic analyses were conducted by Itoh et al.
(2011) on an Al-rich, layered, barred olivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion Click on Term to Read More chondruleRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
from NWA 1152 in an effort to constrain the parent body thermal history. Olivine, spinelMg-Al oxide, MgAl2O4, found in CAIs.
, and Al-rich diopside grains examined in the host barred olivine chondrule reveal slightly different O-isotopic values compared to those determined for silicates composing the igneous rim, suggesting multiple heating events occurred. The measured 26
Mg excess in spinel grains is consistent with chondrule formation at least ~2 m.y. after CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More
, while the lack of such an excess in Al-rich diopside grains indicates an even later crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. Click on Term to Read More
Northwest Africa 1152 could prove to be a key piece in resolving the parent body conundrum that exists for these anomalous meteorites. The specimen shown above is a tiny cut fragment weighing 10 mg, while the photo below shows a large portion of this unusual carbonaceous chondrite in the Fernlea Collection of Rob Elliott.
Photo courtesy of R. Elliott