AcapulcoitePrimitive achondrite that belongs to a small group named after the Acapulco meteorite that was observed to fall in Mexico in 1976. Acapulcoites are made mostly of fine-grained olivine (Fo3-14), orthopyroxene(En86-97), Ca-rich pyroxene (En51Wo44), plagioclase (An12-31), Ni-Fe metal, and troilite. They are transitional between primordial chondritic matter and more differentiated Acapulcoite–LodraniteRare type of primitive achondrite named after the Lodran meteorite that fell in Pakistan in 1868. Initially, lodranites were grouped with the stony-iron meteorites because they contain silicates (olivine, orthopyroxene, and minor plagioclase) and Fe-Ni metal in nearly equal proportions. However, since discovery of the closely related acapulcoite group, lodranites Clan
Purchased June 2002 no coordinates recorded A small 23 g weathered stone was purchased in Agadir, Morocco by Moroccan dealer A. Habibi on behalf of American collector N. Oakes. A portion of 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 was submitted for classification to the University of Washington in Seattle (A. Irving and S. Kuehner), and it was initially classified as a winonaitea partially differentiated asteroid that was disrupted just as it began to form an Fe core and a silicate-rich crust. This disrupting impact mixed silicates into molten Ni-Fe metal forming the silicated IAB irons, and mixed olivine-rich residues of partial melts into unmelted silicates, forming the winonaites. A few winonaites (MetBull 88); however, this classification was eventually changed. Northwest Africa 1617 is composed primarily of magnesian bronzite and forsteritic 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, along with minor FeNi-metal, troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites., chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups., and sodic 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.
The classification as a winonaite was based on those components in NWA 1617 which represent a high degree of 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, such as is manifest in the lack of daubréelite and the occurrence of very Cr-rich chromite. More oxidizingOxidation 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 conditions are consistent with the later-crystallizing, silicate-dominated inclusions of the high-Ni IAB irons, whereas more reducingOxidation 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 conditions are expected to prevail in the graphite–troilite inclusions that predominate among the later crystallizing, low-Ni IAB irons. Also significant is the fact that the Ni content of metalElement that readily forms cations and has metallic bonds; sometimes said to be similar to a cation in a cloud of electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. A diagonal line drawn in these irons was found to be positively correlated with the contents of fayalitePure* iron end-member (Fe2SiO4) of the olivine solid solution series and an important mineral in meteorites. When iron (Fe) is completely substituted by magnesium, it yields the the pure Mg-olivine end-member, forsterite (Mg2SiO4). The various Fe and Mg substitutions between these two end-members are described based on their forsteritic (Fo) and daubréelite (Benedix et al., 1995), consistent with what is found in NWA 1617. The plagioclase composition of NWA 1617 (Ab81) is almost identical to that found in the NWA 1457 winonaite. Likewise, the O-isotopic composition of NWA 1617 plots close to the winonaite group. Therefore, it was proposed that NWA 1617 was an unusual winonaite that extends the compositional limits of the winonaite/IAB iron group.
Notably, in the initial analysis it was found that the silicates in NWA 1617 are more FeO-rich (Fa11.6, Fs11.2) than those in typical winonaites (the most FeO-rich winonaite previously studied is Fa5.3, although silicateThe most abundant group of minerals in Earth's crust, the structure of silicates are dominated by the silica tetrahedron, SiO44-, with metal ions occurring between tetrahedra). The mesodesmic bonds of the silicon tetrahedron allow extensive polymerization and silicates are classified according to the amount of linking that occurs between the inclusions in the IAB-related iron Udei Station are compositionally close [Fa8, Fs9]). In fact, the values are more consistent with those of acapulcoitesPrimitive achondrite that belongs to a small group named after the Acapulco meteorite that was observed to fall in Mexico in 1976. Acapulcoites are made mostly of fine-grained olivine (Fo3-14), orthopyroxene(En86-97), Ca-rich pyroxene (En51Wo44), plagioclase (An12-31), Ni-Fe metal, and troilite. They are transitional between primordial chondritic matter and more differentiated. In 2005, a method to distinguish acapulcoites from winonaites was devised by Rumble III et al. (2005). They utilized a diagram comparing the Fa mol% of olivine vs. the Δ17O‰, and on this diagram NWA 1617 (Fa11.6; Δ17O = –0.86 [±0.02] ‰) plots well within the acapulcoite field close to Monument Draw. Northwest Africa 1617 has now been reclassified as an acapulcoite (MetBull 90). The average grain size of NWA 1617 is 350 µm, which distinguishes it from the more slowly cooled lodranite component of this 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. which are distinguished by grain sizes larger than 500 µm. However, with many new members it is now evident that a continuum exists for the grainsizes of these two groups, and it has been proposed by Bunch et al. (2011) that an arbitrary group division is no longer justified; the term ‘acapulcoite–lodranite clan’ should therefore be applied to all members of the combined group.
For more complete amd current formation scenarios of the acapulcoite–lodranite parent body, visit the Monument Draw and Lodran pages. The specimen of NWA 1617 shown above is a 0.53 g partial slice. The photo below shows a cut face of the main massLargest fragment of a meteorite, typically at the time of recovery. Meteorites are commonly cut, sliced or sometimes broken thus reducing the size of the main mass and the resulting largest specimen is called the "largest known mass". of this small stone. Photo courtesy of N. Oakes—Meteorites–R–Us