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NWA 869 L-Chondrite Meteorites

The sectioned specimen depicted above illustrates the brecciated and chondritic textures of NWA 869.
NWA 869 is a stony meteorite found in Northwest Africa during the year 2000 or 2001 at an undisclosed location near Tindouf in Algeria. NWA 869 is a type of stony meteorite most broadly classified as a chondrite by virtue of containing small spherical inclusions called chondrules. Current evidence and models suggest chondrules formed from preexisting grains that were subsequently reheated to their melting point. The melted grains then combined with one another to form chondrules, remaining in a liquid state for only a brief time before solidifying and accreting with material from other parts of the solar nebula, forming the matrix in which the chondrules are found.

NWA 869 is interesting material from a scientific perspective. It is a breccia from the surface of its parent body and contains fragments of many meteorite types. It is primarily L-type chondrite of differing petrologic grades, but some fragments of carbonaceous, achondritic and other meteorite types that impacted the L parent body are present in NWA 869 as well.

About 80% of all meteorites that fall to Earth are ordinary chondrites, which are distinguished and classified by their total iron and total metal content. Ordinary chondrites are sub-divided as H-Chondrites (high iron), L-Chondrites (low iron) and LL-Chondrites (low iron and low metal). Approximately 45% of the ordinary chondrites are type L-Chondrites, which are sufficiently low in free iron content that they are not strongly attracted to a magnet.

Individual stones of this meteorite vary quite widely in their characteristics, making further classification difficult. Some individuals show what appear to be dark, carbonaceous inclusions and may be clearly brecciated, while other specimens lack these features. NWA 869 is likely paired (actually the same fall) with a number of other NWA meteorites, although reconciling these disparate names would require a systematic survey that has yet to be performed.

NWA 869 has been variously classified by different institutions as differing varieties of L-Chondrite including L3, L4, L5, and L6, with several of these classifications also stating that it is brecciated. Complicating the classification of this meteorite is the likelihood that some stones designated and represented as NWA 869 are actually parts of different Northwest Africa falls altogether.

NWA 869 was officially published in Meteoritical Bulletin #90 in 2006 and classified as an ordinary chondrite that is a breccia of components ranging from petrologic type L4 to type L6 with a shock rating of S3 and a weathering level of W1. Type L4 designates chondrites that are characterized by abundant chondrules, and have been metamorphosed under conditions sufficient to homogenize olivine compositions and recrystallize fine-grained matrix. Type L6 designates chondrites that have been metamorphosed under conditions sufficient to homogenize all mineral compositions, convert all low-Ca pyroxene to orthopyroxene, coarsen secondary phases such as feldspar to sizes =50 m, and obliterate many chondrule outlines. A shock rating of S3 indicates weakly to moderately shocked by collision with other objects in space. A weathering level of W1 indicates minor oxide rims around metal and troilite and minor oxide veins present in polished specimen surfaces.

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