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 Polymict, noncumulate (Main Group–Nuevo Laredo trend)
Found January 1984 30° 19′ S., 126° 37′ E.
This polymict brecciaGeneral term for all breccias that are neither monomict nor dimict. Modified from image source: http://www.saharamet.com/meteorite/gallery/HED/index.html. was found on the Nullarbor Plain of Western Australia by Mrs. J. C. Campbell after she spotted a 503 g specimen from a moving vehicle while travelling cross-country. Eleven additional stones were recovered in July 1985 during a subsequent search of the site, located 200 m west of Camel Donga. Later search parties recovered more stones within the 1 km² area bringing the total known weight to over 2.92 kg.
Camel Donga is a product of fractional crystallizationA crystallization process in which minerals crystallizing from a magma are isolated from contact with the liquid. It is a key process in the formation of igneous rocks during the process of magmatic differentiation. Also known as crystal fractionation. within a magmaMolten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. source and is composed of a mixture of pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category. and 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 in a 3:2 ratio. The fine-grained gray matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. contains gabbroic and doleritic clasts. It contains an unusually high content of total Fe (18.6%), second only to that of NWA 4269 (23.18%). The groundmass 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 has a high metallic iron content of ~2 wt% (~1 vol%) with grain sizes typically ranging from 5 to 10µm., while Fe is also present as finely dispersed particles in silicates. Because of the near absence of Ni (and other siderophile elements) in this metallic iron, it was hypothesized that it formed by in situreductionOxidation 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 of the ferrosiliteA mineral that is composed of Fe-rich pyroxene, FeSiO3. It is the iron endmember of the pyroxene silicate mineral series – enstatite (MgSiO3) to ferrosilite (FeSiO3). (FeSiO3) component of pyroxene during in situ thermal impact metamorphism (Palme et al., 1988). Data from Hf/W ratios indicate that this thermal metamorphism occurred ~10–15 m.y. after mantleMain silicate-rich zone within a planet between the crust and metallic core. The mantle accounts for 82% of Earth's volume and is composed of silicate minerals rich in Mg. The temperature of the mantle can be as high as 3,700 °C. Heat generated in the core causes convection currents indifferentiationA process by which a generally homogeneous chondritic body containing mostly metal, silicates and sulfides will melt and form distinct (differentiated) layers of different densities. When the melting process continues for a long enough period of time, the once chondritic body will re-partition into layers of different composition including, long after the extinctionIn astronomy, the dimming of starlight as it passes through the interstellar medium. Dust scatters some of the light, causing the total intensity of the light to diminish. It is important to take this effect into account when measuring the apparent brightness of stars. The dark bands running across portions of the major radiogenic elements. This scenario constrains the cause of the heating event to a major impact on VestaThird largest and fourth brightest asteroid; it was discovered in 1807 by Heinrich Olbers and named for the ancient Roman goddess of the hearth. 4 Vesta has a basaltic surface composition and an average density not much less than that of Mars. Evidently lava once flowed here indicating that the (Kleine et al., 2004). A similar impact event is thought to have produced the pure Fe-metal in the 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 NWA 6601 (Agee, 2011).
Conversely, in their study of Camel Donga, Warren and Isa (2015) found a lack of evidence for significant reduction in either the silicates or the Fe-oxides, of which the latter are considered to be the more susceptible to 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 agents. In addition, Warren et al. (2017) identified several cm-scale, metal-rich (12–17 vol%), ovoid 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 nodules (see photo below) and other nearby 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 aggregates which are enriched in Ni relative to most other Fe-metal phases in the meteorite. These nodules are also enriched in trace siderophile elements and lack other evidence for in situ reduction. It was concluded that the metal nodules reflect the addition of an impactor component to the material that was precursory to Camel Donga. In view of these findings, it was proposed that the present composition of Camel Donga (in a similar manner to the eucrite NWA 5738) reflects a two-stage process of metasomatic alteration by a reducing fluid that originated as a metal- and volatile-rich carbonaceous-chondritic (e.g., CM-type) contaminant. It was speculated by Warren et al. (2017) that an initial impact-generated reduction process involving a S2– and CO-rich fluid derived from the exogenous nodules or other impactor material led to the production of troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites.. Subsequent metasomatism involving H2O-rich fluids initiated a reaction with the existing troilite to produce the near-pure Fe-metal component in Camel Donga and NWA 5738 (see diagram below). Camel Donga ovoid nodule 11 mm wide in a 9g section; FoV 22 mm
Photo and diagram credit: Warren et al., MAPS, vol. 52, #4, (2017) ‘Secondary-volatiles linked metallic iron in eucritesMost 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: The dual-origin metals of Camel Donga’ (http://dx.doi.org/10.1111/maps.12827) Camel Donga has an absolute crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. age based on the Pu–Xe chronometer of 4.507 b.y., and it has a cosmic-ray exposure ageTime interval that a meteoroid was an independent body in space. In other words, the time between when a meteoroid was broken off its parent body and its arrival on Earth as a meteorite - also known simply as the "exposure age." It can be estimated from the observed effects of 36.6 (±1.4) m.y., including it within one of the five common breakup events occurring 6 (±2), 12 (±2), 21 (±4), 38 (±8), and 73 (±3) m.y. ago. The pristine condition of these stones is evidence of a recent 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, and it is inferred from their shapes that a single fragmentation was followed by flight orientation of many of the individuals. The occurrence of regmaglypts, radial flow lines, and melt overflow is a common characteristic of many of the stones. The Camel Donga specimen pictured above is a 21.8 g individual with a cut face. The photo below shows the brecciated interior of this eucrite.