NWA 1827

MesosideriteOne of two main types of stony-iron meteorite, the other being pallasites. Mesosiderites are a mixture of approximately 50% basaltic, gabbroic and orthopyroxenitic silicates and 50% Ni-Fe metal and sulfides. The name derives from the Greek "mesos" meaning "middle" or "half" and "sideros" for "iron;" hence "half-iron". The silicates are, group 2C

Purchased June 2002
no coordinates recorded A complete, fusion-crusted, stony-iron meteoriteMeteorite composed of roughly equal amounts by weight of silicate minerals and Ni-Fe metal. The stony-irons consist of two groups: mesosiderites and pallasites. However, there is gradual shading into metal-rich stony meteorites such as the lodranites (once considered stony-irons) and silicate-rich iron meteorites. Stony-iron meteorites are less abundant than their, weighing 877 g, was purchased in Risani, Morocco on behalf of an American collector. A polished thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope. from NWA 1827 was prepared for analysis at the Department of Earth and Space Sciences, University of Washington (A. Irving and S. Kuehner). Optical petrography, energy dispersive electron microprobeInstrument that analyzes the chemistry of very small spots by bombarding the sample with a focused electron beam and measuring the X-rays produced. The amount and energy of the x-rays indicate the chemical composition of the sample. The electron microprobe is an important tool used in determining the composition of analyses, and quantitative microprobe analyses were utilized in the initial analysis of this 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. Comparative studies of NWA 1827 with NWA 1879 and other independently owned masses (NWA 1882, 1912, 1951, 1982, 3055, and 1645) show that close similarities exist among them, and all of these masses, totaling at least 26.4 kg, are presumed to be paired (Bunch et al., 2004). Continued research was conducted by the Bunch et al. (2014) on these specimens and a large number of mesosiderite samples previously considered to represent a separate fallMeteorite seen to fall. Such meteorites are usually collected soon after falling and are not affected by terrestrial weathering (Weathering = 0). Beginning in 2014 (date needs confirmation), the NomComm adopted the use of the terms "probable fall" and "confirmed fall" to provide better insight into the meteorite's history. If. It was eventually determined that all of these mesosiderites represent a single strewn fieldArea on the surface containing meteorites and fragments from a single fall. Also applied to the area covered by tektites, which are produced by large meteorite impacts. Strewnfields are often oval-shaped with the largest specimens found at one end. Given that the largest specimens go the greatest distance, a meteoroid's (totaling at least 80 kg) comprising mesosiderites of differing subgroups (see also NWA 1878).

The general appearance of NWA 1827 was found to be similar to that of a mesosiderite, exhibiting an equilibrated, igneous texture, and consisting primarily 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 and abundant 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, along with minor 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 merrillite, and rare anorthiteRare compositional variety of plagioclase and the calcium end-member of the plagioclase feldspar mineral series with the formula CaAl2Si2O8. Anorthite is found in mafic igneous rocks such as anorthosite. Anorthite is abundant on the Moon and in lunar meteorites. However, anorthite is very rare on Earth since it weathers rapidly. However, NWA 1827 was inconsistent with a classification as a mesosiderite for several reasons. It has a lower metal content than other mesosiderites (~10 vol% vs. ~50% [~17–90 wt%]), and the metal has a lower Ni content than typical mesosiderites (5 wt.% vs. 7.5–10%). The Fs content of the largest orthopyroxene grains is bronzitic (Fs16.2), with that of the average-sized orthopyroxene grains being somewhat higher (Fs22.5–Fs27.3). This Fs range is significantly lower than that of typical mesosiderites (Fs20–Fs40); however, orthopyroxenes in this range are found in diogenitesDiogenites belong to the evolved achondrite HED group that also includes howardites and eucrites. They are named after the Greek philosopher Diogenes of Apollonia, of the 5th century BCE, who was the first to suggest that meteorites come from outer space (a realization forgotten for over 2,000 years). They are. The 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 content (~2%) is also lower than that of other mesosiderites, with the exception of the single 2C member, RKPA79015; again, anorthitic plagioclase in this abundance is found in some diogenites. The FeO/MnO ratio of the orthopyroxene grains in NWA 1827 (29.7–34.8) is higher than that of most mesosiderites, but do fall in the range of diogenites. Finally, NWA 1827 lacks 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 and chromite, common constituents in mesosiderites.

Based on a preliminary analysis, it was proposed that the data best fit a classification as a recrystallized, metal-rich diogeniteDiogenites belong to the evolved achondrite HED group that also includes howardites and eucrites. They are named after the Greek philosopher Diogenes of Apollonia, of the 5th century BCE, who was the first to suggest that meteorites come from outer space (a realization forgotten for over 2,000 years). They are, which was intruded by an exotic metallic body and annealed within a deep regolithMixture of unconsolidated rocky fragments, soil, dust and other fine granular particles blanketing the surface of a body lacking an atmosphere. Regolith is the product of "gardening" by repeated meteorite impacts, and thermal processes (such as repeated heating and cooling cycles).  . However, further analysis conducted at the Northern Arizona University (T. Bunch) of a larger area of this heterogeneous mesosiderite revealed sparse 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 and diogeniteDiogenites belong to the evolved achondrite HED group that also includes howardites and eucrites. They are named after the Greek philosopher Diogenes of Apollonia, of the 5th century BCE, who was the first to suggest that meteorites come from outer space (a realization forgotten for over 2,000 years). They are inclusions, and has led to the conclusion that NWA 1827 is most similar to a mesosiderite of the 2C subgroup, the second such mesosiderite after RKPA79015.

The difficulty in determining that NWA 1827 is actually a mesosiderite was similarly felt by Clark and Mason (1982) in their attempt to classify RKPA79015 (Haack et al., 1996). They found that the amount of tetrataenite present in meteorites with comparable bulk Ni concentrations increases with decreasing cooling rate from 500 to 250°C. Therefore, tetrataenite rims on taeniteLess common than kamacite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Taenite, γ-(Fe,Ni), has 27-65 wt% Ni, and forms small crystals that appear as highly reflecting thin ribbons on the etched surface of a meteorite; the name derives from the Greek word for "ribbon." grains are much wider in mesosiderites (typically 10–20 µm) than in 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 (2–5 µm) and iron meteorites (less than or equal to 2 µm) that have comparable bulk Ni concentrations (Clark and Scott, 1980; Hassanzadeh et al., 1990). Clark and Mason were able to classify RKPA79015 as a mesosiderite on the basis of this feature. The photo of NWA 1827 shown above is an 11.94 g end section. Excellent photos of a large section of NWA 1827 can be seen at meteoritesaustralia.com.