AngriteType of evolved achondrite meteorite that represent some of the earliest stages of asteroidal differentiation and magmatism in our solar system. Angrites are named for the Angra dos Reis meteorite, which fell in Rio de Janeiro, Brazil, in early 1869. They are basaltic (mafic) rocks, often containing porous areas, and Click on Term to Read More
Found spring 2001
no coordinates recorded A single 810 g stone was found in the Moroccan Sahara and subsequently sold to a dealer in Bouarfa, Morocco. The dark-gray, shiny fusion crustMelted exterior of a meteorite that forms when it passes through Earth’s atmosphere. Friction with the air will raise a meteorite’s surface temperature upwards of 4800 K (8180 °F) and will melt (ablate) the surface minerals and flow backwards over the surface as shown in the Lafayette meteorite photograph below. Click on Term to Read More is very thin but well-preserved, suggesting a relatively 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 Click on Term to Read More. Northwest Africa 1296 was analyzed at multiple laboratories in France (Université d’Angers and Université Pierre & Marie Curie) and determined to be a member of the rare angriteType of evolved achondrite meteorite that represent some of the earliest stages of asteroidal differentiation and magmatism in our solar system. Angrites are named for the Angra dos Reis meteorite, which fell in Rio de Janeiro, Brazil, in early 1869. They are basaltic (mafic) rocks, often containing porous areas, and Click on Term to Read More group (Jambon et al., 2002).
An account of the mineralogy and petrologyScience dealing with the origin, history, occurrence, chemical composition, structure and classification of rocks. Click on Term to Read More
of NWA 1296 was published by Jambon et al.
(2005). The major minerals in NWA 1296 include anorthitic 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 Click on Term to Read More
(32 vol%), strongly zoned grains of the clinopyroxene Al,Ti–diopside-hedenbergite, formerly known as fassaite (34 vol%), strongly zoned Ca-rich 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
(28 vol%), and kirschsteinite (3 vol%)—a characteristic mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous Click on Term to Read More
present in most angrites. Other minor constituents include pyrrhotiteIron sulfide group of minerals whose composition ranges widely between its end members pyrrhotite (Fe7S8) whose crystal structure is monoclinic, and troilite (FeS) whose crystal structure is hexagonal. Its general formula is Fe1−xS (where x = 0 to 0.17). The troilite phase is found mainly in meteorites and in the Click on Term to Read More
, F-bearing apatite, ulvöspinelMg-Al oxide, MgAl2O4, found in CAIs.
, and possibly Ca silico-apatite similar to that found in D’Orbigny, Sah 99555, NWA 4590, and Asuka 881371. Calcium enrichment is a common feature of this group. Trace elementSubstance composed of atoms, each of which has the same atomic number (Z) and chemical properties. The chemical properties of an element are determined by the arrangement of the electrons in the various shells (specified by their quantum number) that surround the nucleus. In a neutral atom, the number of Click on Term to Read More
and REEOften abbreviated as “REE”, these 16 elements include (preceded by their atomic numbers): 21 scandium (Sc), 39 Yttrium (Y) and the 14 elements that comprise the lanthanides excluding 61 Promethium, an extremely rare and radioactive element. These elements show closely related geochemical behaviors associated with their filled 4f atomic orbital. Click on Term to Read More
data for NWA 1296 are similar to that for the other quenched angrites, indicating a common magmatic origin (Sanborn and Wadhwa, 2010). The average Pb–Pb date of 4.56420 (±0.00045) b.y. for NWA 1296 provides a minimum estimate for its 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
age, which is also consistent with the ages derived for D’Orbigny and Sahara 99555 (Amelin and Irving, 2011).
Although it has a mineralogy that is typical of the angrite group, this angrite exhibits a very fine-grained texture that is different from the other angrites, one which is consistent with rapid quenching (see interior view on the NAU webpage
). Northwest Africa 1296 consists of µm-sized, branched olivine crystals that form the cores of mineral chains, with 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 Click on Term to Read More
crystals associated with these olivines. These chains are incorporated into later crystallizing clinopyroxene crystals. Other polycrystalline olivines, associated with kirschsteinite, formed outside of the mineral chains as the crystallization sequence culminated with clinopyroxene and accessory phases such as the opaques. Some pyrrhotite globules contain exsolved 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 Click on Term to Read More
, while others contain inclusions of quenched Ca-carbonate melt. Small vugs are present among these final crystallization phases, some of which contain this primary Ca-carbonate similar to that present in D’Orbigny vesicles.
The composition and texture of NWA 1296 is consistent with an origin involving ~15% partial meltingAn igneous process whereby rocks melt and the resulting magma is comprised of the remaining partially melted rock (sometimes called restite) and a liquid whose composition differs from the original rock. Partial melting occurs because nearly all rocks are made up of different minerals, each of which has a different melting Click on Term to Read More
of a peridotite influenced by a high carbonateMineral or compound containing carbon and oxygen (i.e. calcium carbonate, CaCO3, calcite). Click on Term to Read More
content, which resulted in low silicaSilicon dioxide, SiO2.
contents and high Ca to Al ratios characteristic of angrites. 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. Click on Term to Read More
occurred followed by secondary impact-melting, loss of volatiles, and mixing of olivine xenocrysts into some angrite members (rare or absent in NWA 1296); thereafter, rapid cooling ensued.
Jambon et al.
(2005) argue that since the end path of crystallization is kirschsteinite rather than silica, angrites cannot be considered to be basaltic rocks. In addition, they demonstrate that derivation from a CV- or CM-like source cannot be reconciled with angrite compositional factors, such as coreIn the context of planetary formation, the core is the central region of a large differentiated asteroid, planet or moon and made up of denser materials than the surrounding mantle and crust. For example, the cores of the Earth, the terrestrial planets and differentiated asteroids are rich in metallic iron-nickel. Click on Term to Read More
formation, the presence of highly magnesian olivines in some members, low silica and alkali contents, the presence of carbonates in the melt, and unique oxygenElement that makes up 20.95 vol. % of the Earth's atmosphere at ground level, 89 wt. % of seawater and 46.6 wt. % (94 vol. %) of Earth's crust. It appears to be the third most abundant element in the universe (after H and He), but has an abundance only Click on Term to Read More isotopeOne of two or more atoms with the same atomic number (Z), but different mass (A). For example, hydrogen has three isotopes: 1H, 2H (deuterium), and 3H (tritium). Different isotopes of a given element have different numbers of neutrons in the nucleus. Click on Term to Read More
ratios. A contrary conclusion based on partial-melting experiments and Rb–Sr systematics supports the derivation of angrites from CV3-type precursor material. A different scenario for the petrogenesis of the angrites has been presented by Kurat et al.
(2004), a brief synopsis of which can be found on the D’Orbigny
page. They provide compelling evidence for a non-igneous origin of the angrites on a very early-formed 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
, one which was composed primarily of refractory condensateIn the solar nebula, product of a chemical condensation reaction where a mineral phase precipitates (condenses) directly from a cooling vapor. Click on Term to Read More
A limited number of unique angrites are represented in our collections today which have been grouped as basaltic/quenched, sub-volcanic/metamorphic, or plutonicGeology: Igneous intrusive body that forms when magma is injected into host rocks and solidifies. Plutons occur in the crust of asteroids undergoing differentiation or planets. Named after Pluto, the Roman god of the underworld. Plutonic rocks are the rocks found within a pluton. Astronomy: Category of planet including all Click on Term to Read More
/metamorphic, along with a single dunitic sample NWA 8535 (photo
courtesy of Habib Naji). Another quenched angrite, NWA 7203 (photo
courtesy of Labenne Meteorites), exhibits a striking variolitic texture. Portions of the angrite asteroid must be in a stable orbitThe elliptical path of one body around another, typically the path of a small body around a much larger body. However, depending on the mass distribution of the objects, they may rotate around an empty spot in space • The Moon orbits around the Earth. • The Earth orbits around Click on Term to Read More
(planetary or asteroid beltBelt located between 2.12 and 3.3 AU from the Sun and located between the orbits of Mars and Jupiter containing the vast majority of asteroids. The asteroid belt is also termed the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such Click on Term to Read More
) from which spallationThe formation of new nuclides by interactions of high-energy cosmic ray protons with target nuclei that commonly produce several smaller product nuclides.
has continued to occur over the past ~56 m.y. as indicated by the broad range
in angrite CRE ages.
Interestingly, small fine-grained basaltBasalt is the most common extrusive igneous rock on the terrestrial planets. For example, more than 90% of all volcanic rock on Earth is basalt. The term basalt is applied to most low viscosity dark silicate lavas, regardless of composition. Basalt is a mafic, extrusive and fine grained igneous rock Click on Term to Read More
clasts exhibiting textures and mineralogy generally consistent with a quenched angrite-like impactor are preserved in impact melt glass fragments recovered from the significant impact event that occurred ~5.28 m.y. ago near Bahía Blanca, Argentina (Schultz et al.
, 2006; Harris and Schultz, 2009, 2017; see top photo below). The photo of NWA 1296 shown above is a 1.1 g partial slice, while those below show 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". Click on Term to Read More
Photo credit (left): Schultz et al.
, vol. 41, #5, p. 755 (2006) (http://dx.doi.org/10.1111/j.1945-5100.2006.tb00990.x)
Diagram credit (right): Harris and Schultz, 40th LPSC, #2453
Photo credit: A. Jambon
Photo credit: Jambon et al.
, vol. 40, #3, p. 362 (2005)