R chondriteChondrites 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 Click on Term to Read MorebrecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Click on Term to Read More, rumurutiiteMember of a rare group of chondrites, formerly named the Carlisle Lakes group, after a meteorite found in Australia in 1977. It is now named for the type specimen Rumuruti that fell in Kenya, Africa, in 1934. Rumuruti is the only witnessed fall of this group and only one small (tentative classification) (possibly paired with NWA 4814) click on photo for a magnified view Found before 2007 no coordinates recorded Many possibly paired stones and fragments representing a unique rumurutiite are thought to be distributed in both Europe (300 g stone) and the United States (400 g fragments). The specimen shown above is reportedly from a lot of two large, fresh, partially fusion-crusted stones weighing together 2,635 g, acquired by American collectors/dealers. A type sample from one or more of these stones was sent to Northern Arizona University for analysis, assignment of a provisional NWA-series number, and classification; however, the exact provenance for the specimen shown above has been lost. As photographed, the specimen above exhibiting pronounced dark and lighter lithologies bears a strong resemblance to both the 300 g R3–6 NWA 2943 found in 2005, and to the 1,120 g R4 [R3–6] chondrite NWA 4814 found in 2006, either of which might or might not share a common source 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 Click on Term to Read More. A search for more information on these meteorites could help determine whether they derive from a common meteorite, or perhaps are launch paired.
This rumurutiite exhibits clasts representing a wide variety of petrologic types. Dark, highly unequiliberated clasts containing distinct chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More represent type 3 material, while lighter clasts are more highly metamorphosed and represent petrologic types possibly as high as 6. A modified version of the Van Schmus–Wood classification scheme has been proposed by Berlin and Stöffler (2004) to accommodate the R chondrite metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. Click on Term to Read More variation present in the 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 Click on Term to Read More, feldsparAn alumino-silicate mineral containing a solid solution of calcium, sodium and potassium. Over half the Earth’s crust is composed of feldspars and due to their abundance, feldspars are used in the classification of igneous rocks. A more complete explanation can be found on the feldspar group page. Click on Term to Read More, and sulfides, especially the lack of low-Ca pyroxene in types 5 and 6:
Modified Van Schmus–Wood Classification Scheme For R 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 Click on Term to Read More
3
4
5
6
Homogeneity of 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
>5% mean deviation
homogenous
homogenous
homogenous
Pyroxene
predominantly low-Ca pyroxene
low-Ca and Ca-rich pyroxene
only Ca-rich pyroxene
only Ca-rich pyroxene
Feldspar
small glassy intergrowths
isolated intergrowths
networks forming
well-developed networks
Sulfides
even distribution
even distribution
even distribution
mobilized
A more comprehensive look at the rumurutiite chondrite group can be found on the DaG 013 page. The photo shown above is a 1.89 g slice exhibiting a range of petrologic types in this R chondrite breccia.
R5, rumurutiiteMember of a rare group of chondrites, formerly named the Carlisle Lakes group, after a meteorite found in Australia in 1977. It is now named for the type specimen Rumuruti that fell in Kenya, Africa, in 1934. Rumuruti is the only witnessed fall of this group and only one small Found 2005 coordinates not recorded A large 23.62 kg stone covered by a thin, translucent, olive-gray crustOutermost layer of a differentiated planet, asteroid or moon, usually consisting of silicate rock and extending no more than 10s of km from the surface. The term is also applied to icy bodies, in which case it is composed of ices, frozen gases, and accumulated meteoritic material. On Earth, the Click on Term to Read More, and not considered to be a 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 Click on Term to Read More, was gifted by a meteorite collector to T. Stout. In June 2012, a portion was sent to Cascadia Meteorite Laboratory in Oregon (A. Ruzicka and M. Hutson) for analysis, and it was determined that the stone was a meteorite after all—the largest R5 chondriteChondrites 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 Click on Term to Read More known, designated NWA 7514.
The interior of this fresh R chondrite appears homogeneous and somewhat featureless in hand section, with an overall gray color. In thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope., chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More are evident but indistinct, embedded in a transparent matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More. Features are consistent with a shock stageA petrographic assessment, using features observed in minerals grains, of the degree to which a meteorite has undergone shock metamorphism. The highest stage observed in 25% of the indicator grains is used to determine the stage. Also called "shock level". Click on Term to Read More in the range of S2–S4, and the meteorite is virtually unweathered, reflecting the weathering index (wi) value of 0 (Rubin and Huber, 2005). In contrast to some R 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 Click on Term to Read More which have experienced significant aqueous alteration of their sulfide minerals (mainly 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 and pentlanditeFe-Ni sulfide, (Fe,Ni)9S8, that is often associated with troilite, and found in the matrix and chondrules of CO, CV, CK and CR chondrites. The color is yellow-bronze with light bronze-brown streak and metallic luster. It typically forms during cooling of magmatic sulfide melts during the evolution of parent silicate melt. The Click on Term to Read More) and contain abundant hydrous phases and brown staining (e.g., amphibole, phlogopite, and apatite in LAP 04840 and MIL 11207; Gross et al., 2013, 2017), the sulfides in NWA 7514 are virtually unaltered, reflecting a formation in dry conditions and a lack of terrestrial aqueous alteration (Ruzicka et al., 2013).
An oxygen three-isotope diagram was prepared from values determined at The Open University, United Kingdom (R. Greenwood), and the plot falls within the Rumuruti-chondrite field. The R-chondrite group is considered to be one of the most oxidizedOxidation 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 Click on Term to Read More groups of meteorites, and NWA 7514 has the highest Δ17O value of any R chondrite measured to date. The specimen of NWA 7514 shown above is a 0.73 g partial slice. The photo below shows the unusual and awesome 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 courtesy of Tim Stout and Rob Wesel—Nakhla Dog Meteorites
R5, rumurutiiteMember of a rare group of chondrites, formerly named the Carlisle Lakes group, after a meteorite found in Australia in 1977. It is now named for the type specimen Rumuruti that fell in Kenya, Africa, in 1934. Rumuruti is the only witnessed fall of this group and only one small Purchased October 2002 coordinates not recorded A very fresh 710 g stone with black 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 was found in Morocco or Algeria. It was subsequently purchased in Denver from a Moroccan dealer by D. Gregory. Analysis and classification was completed at the Department of Earth and Space Sciences, University of Washington (A. Irving and S. Kuehner), and 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 Click on Term to Read More, named NWA 1668, was determined to be an R5 genomict brecciaWork in Progress ... A rock that is a mechanical mixture of different minerals and/or rock fragments (clasts). A breccia may also be distinguished by the origin of its clasts: (monomict breccia: monogenetic or monolithologic, and polymict breccia: polygenetic or polylithologic). The proportions of these fragments within the unbrecciated material Click on Term to Read More.
As is typical for R 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 Click on Term to Read More, chondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More are more sparsely distributed than in other chondrites. They have an average diameter of ~0.3 mm, which is larger than those in CO3 chondrites and smaller than those in ordinary chondrites (Imae and Zolensky, 2003), a size consistent with what is expected to occur at large heliocentricCentered around a sun. Our own Solar System is centered around the Sun so that all planets such as Earth orbit around the Sun. Note that 25% of Americans incorrectly believe the Sun revolves around the Earth. Click on Term to Read More distances. With respect to mineralogy, NWA 1668 is primarily composed of 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 (Fa38.9), clinopyroxene, 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 Click on Term to Read More, troiliteBrass colored non-magnetic Fe sulfide, FeS, found in a variety of meteorites., and Ti-chromite, along with minor 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 Click on Term to Read More, and rare, high-Ni 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 (awaruiteNi-rich Fe metal, Ni3Fe, similar to taenite found in minor amounts in some meteorites. Awaruite is also known as josephinite, a mineral found as placer deposits in Josephine County, Oregon, and sometimes mistaken for a meteorite. Note: web.mineral.com incorrectly defines Awaruite as “Ni2Fe to Ni3Fe”, however the IMA Database of Click on Term to Read More, composed of 72% Ni). The sparsity of metal, or lack thereof in some R chondrites, indicates that R chondrites experienced highly 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 Click on Term to Read More conditions, probably both in the nebulaAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive Click on Term to Read More and on the 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.
Parent body metamorphism in an oxidizing, water-rich environment is attested by the hydroxyl-rich minerals amphibole, phlogopite, and apatite present in the R6 chondrites LAP 04840 and MIL 11207. It is considered that these chondrites experienced metamorphism of insoluble organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. Click on Term to Read More matter at high temperatures (~720°C) and at significant depth (tens of km) within a lithologic unit in which water with a high D/H ratio was pervasive. This deep burial is considered to be the result of reassembly following impact disruption on the R chondriteChondrites 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 Click on Term to Read More parent body (McCanta et al., 2006, 2008). In a study of these two hydroxyl-bearing R chondrites, Gross et al. (2017) reasoned that such high abundances of hydrous phases could only be established under conditions of high water vapor pressure (20–700 barUnit of pressure equal to 100 kPa.), and such pressures could only be maintained on this relatively small body through the emplacement of a solid ice shield.
Noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. Click on Term to Read More analyses of the known Northwest Africa R chondrites were conducted by Vogel et al. (2014). Based on the results, they have tentatively placed these numerous R chondrites into ~16 groupings representing possible common source craters and/or 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 events. They have proposed a pairing exists between NWA 1668 and NWA 2897 which show a common CRE age of ~66 m.y.
Northwest Africa 1668 is one of the freshest R chondrites found to date, next to the 1934 fall in Rumuruti and the 23.6 kg NWA 7514. Recently, a more useful weathering index (wi) was developed by Rubin and Huber (2005) for those oxidizedOxidation 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 Click on Term to Read More meteorite groups lacking significant FeNi-metal phases, such as the CK and R chondrite groups. This index is based on the modal abundance of brown-stained silicates as visually determined on a thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope. in transmitted light at ~100× magnification. It is thought that the brown staining in R chondrites (and CK chondrites) is caused by the terrestrial decomposition and mobilization of sulfides (mainly 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 and pentlanditeFe-Ni sulfide, (Fe,Ni)9S8, that is often associated with troilite, and found in the matrix and chondrules of CO, CV, CK and CR chondrites. The color is yellow-bronze with light bronze-brown streak and metallic luster. It typically forms during cooling of magmatic sulfide melts during the evolution of parent silicate melt. The Click on Term to Read More), which are typically prevalent in the R chondrite group as a result of formation in a high-sulfur fugacity; e.g., Rumuruti wi-0 contains 8.0 wt%.
In addition to NWA 1668 and Sah 99527 (both R5), several other unbrecciated R chondrites have been recovered so far, including the following: HaH 119, Ouzina, NWA 053, NWA 800, and Sah 98248 (all R4); NWA 753 (R3.9); Carlisle Lakes and NWA 978 (R3.8); NWA 755 (R3.7); and Acfer 217 (R3.8–5). Further details about the R chondrite group can be found on the DaG 013 page. The photo above shows a 4.0 g partial slice of this rumurutiite.
R3.8, rumurutiiteMember of a rare group of chondrites, formerly named the Carlisle Lakes group, after a meteorite found in Australia in 1977. It is now named for the type specimen Rumuruti that fell in Kenya, Africa, in 1934. Rumuruti is the only witnessed fall of this group and only one small Purchased August 1, 2001 coordinates not recorded Three fragments weighing together 722 g were purchased in Erfoud, Morocco. Classification was performed at UCLA, and Northwest Africa 978 was determined to be an R3.8 chondriteChondrites 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 Click on Term to Read More. Although it was initially assigned a relatively low weathering grade of W2, a more useful weathering index (wi) has since been developed by Rubin and Huber (2005) for those oxidizedOxidation 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 Click on Term to Read MoremeteoriteWork 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 Click on Term to Read More groups lacking significant FeNi-metal phases, such as the CK and R chondrite groups. This index is based on the modal abundance of brown-stained silicates as visually determined on a thin sectionThin slice or rock, usually 30 µm thick. Thin sections are used to study rocks with a petrographic microscope. in transmitted light at ~100× magnification. It is thought that the brown staining in R 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 Click on Term to Read More (and CK chondrites) is caused by the terrestrial decomposition and mobilization of sulfides (mainly 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 and pentlanditeFe-Ni sulfide, (Fe,Ni)9S8, that is often associated with troilite, and found in the matrix and chondrules of CO, CV, CK and CR chondrites. The color is yellow-bronze with light bronze-brown streak and metallic luster. It typically forms during cooling of magmatic sulfide melts during the evolution of parent silicate melt. The Click on Term to Read More), which are typically prevalent in this meteorite group; e.g., Rumuruti wi-0 contains 8.0 wt% sulfides. Northwest Africa 978 was determined to have a weathering index of wi-5, or severely weathered. This meteorite has been weakly shocked (S3).
In their noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. Click on Term to Read More studies, Schultz et al. (2005) suggested pairing several R chondrite finds of similar petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes. with NWA 978 (21Ne-based CRE age of 10.8 (±0.4) m.y.), including NWA 755, NWA 845, NWA 851, and NWA 1471. Subsequent noble gas analyses of the known Northwest Africa R chondrites were conducted by Vogel et al. (2011, 2014). Their ~16 groupings vary slightly from the previous pairings suggested by other investigators, and they propose an ~10 m.y. CRE age group representing possible common source craters and/or 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 events which includes R chondrites with the NWA series designations 755, 845, 851, 978, 1471, 2198, and 5069, and possibly DaG 013.
This is a unique group of chondrites having a higher volume of 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 (FeO-rich), a lower volume 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 Click on Term to Read More, and essentially no FeNi-metal as compared to all other chondrite groups. This is thought to be the result of metasomatic 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 Click on Term to Read More in which FeNi-metal and pyroxene reacted with water to form olivine (Isa et al., 2010). While R chondrites share certain similarities with ordinary chondrites including refractory 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 depletions and siderophile elementLiterally, "iron-loving" element that tends to be concentrated in Fe-Ni metal rather than in silicate; these are Fe, Co, Ni, Mo, Re, Au, and PGE. These elements are relatively common in undifferentiated meteorites, and, in differentiated asteroids and planets, are found in the metal-rich cores and, consequently, extremely rare on abundances, they differ in volatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). element abundances and petrologic trends. The triple increase in Zn relative to ordinary chondrites and the sparsity 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 Click on Term to Read More, or lack thereof, observed in some R chondrites, indicates that this group experienced highly 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 Click on Term to Read More conditions both in the nebulaAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive Click on Term to Read More and on the parent asteroid.
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 metamorphism in an oxidizing, water-rich environment is attested by the hydroxyl-rich minerals amphibole, phlogopite, and apatite present in the R6 chondrites LAP 04840 and MIL 11207. It is considered that these chondrites experienced metamorphism of insoluble organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. Click on Term to Read More matter at high temperatures (~720°C) and at significant depth (tens of km) within a lithologic unit in which water with a high D/H ratio was pervasive. This deep burial is considered to be the result of reassembly following impact disruption on the R chondrite parent body (McCanta et al., 2006, 2008). In a study of these two hydroxyl-bearing R chondrites, Gross et al. (2017) reasoned that such high abundances of hydrous phases could only be established under conditions of high water vapor pressure (20–700 barUnit of pressure equal to 100 kPa.), and such pressures could only be maintained on this relatively small body through the emplacement of a solid ice shield.
The difference in O-isotopic abundances between the R chondrites and the ordinary chondrites is greater than it is among the H, L, and LL ordinary chondriteWork in Progress Ordinary chondrites (OCs) are the largest meteorite clan, comprising approximately 87% of the global collection and 78% of all falls (Meteoritical Society database 2018)1. Meteorites & the Early Solar System: page 581 section 6.1 OC of type 5 or 6 with an apparent shock stage of S1, Click on Term to Read More groups, further resolving the R group from the ordinary chondrite groups (Weber et al., 1997). Similar to carbonaceous chondrites, R chondrites have a high olivine content within a high proportion of matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. Click on Term to Read More, reflecting their highly oxidized nature. Because R chondrites have the highest 17O value of any other Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. material, they plot on a different O-isotope trend line than the other chondrites. This plot is farther from the carbonaceous and enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3). Click on Term to Read More chondrites than it is from the ordinary chondrites (Rubin and Kallemeyn, 1989). Rumuruti chondrites of type 3 contain noble metals such as platinum, osmium, and germanium that originated as nebular condensates. In higher metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. Click on Term to Read More types, the volatile germanium phases are decomposed, while other noble metal phases are transformed into mostly arsenides and tellurides.
In addition to NWA 978 (R3.8), several other unbrecciated R chondrites have been recovered so far, including the following: Sah 99527 and NWA 1668 (both R5); HaH 119, Ouzina, NWA 053, NWA 800, and Sah 98248 (all R4); NWA 753 (R3.9); Carlisle Lakes (R3.8); NWA 755 (R3.7); and Acfer 217 (R3.8–5). The photo above shows a 3.5 g slice of NWA 978, while the top photo below shows the fresh 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 on the 361.6 g 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. The bottom image is an excellent petrographic thin section micrograph of NWA 978, shown courtesy of Peter Marmet. Photo courtesy of Mike Farmer—Mike’s Meteorites and Tektites click on image for a magnified view Photo courtesy of Peter Marmet
R3.9, rumurutiiteMember of a rare group of chondrites, formerly named the Carlisle Lakes group, after a meteorite found in Australia in 1977. It is now named for the type specimen Rumuruti that fell in Kenya, Africa, in 1934. Rumuruti is the only witnessed fall of this group and only one small Found January 2000 coordinates not recorded Multiple fragments weighing together 12 kg were purchased in Rissani, Morocco, while the actual findMeteorite not seen to fall, but recovered at some later date. For example, many finds from Antarctica fell 10,000 to 700,000 years ago. Click on Term to Read More location was probably the Kem Kem region of the Sahara. Classification was performed at the Institut für Planetologie in Münster, Germany. Northwest Africa 753 is a brecciated, very weakly shocked (S2) 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 Click on Term to Read More that is relatively fresh compared to most other R chondriteChondrites 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 Click on Term to Read More finds—designated W2 on the Wlotzka weathering scale (1993). Abundant sulfides, typically pyrrhotites, attest to a S-rich environment of formation (Jackson and Lauretta, 2010). It has been established through laboratory analyses that several pairings to NWA 753 exist, including NWA 1472, 1476, 1477, 1478, and 1566.
Results of Mn–Cr isotopic systematics have established an initial age for NWA 753 of 4.561 (±2) m.y., which is a few m.y. younger than the age established for carbonaceous 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 Click on Term to Read More (~4.566 m.y.) (Jogo et al., 2006). A possible correlation of Cr-isotopic compositions with O-isotopic variations for ordinary and R chondrites has been demonstrated.
In their search for CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More and other Al-rich objects in R chondrites, Rout and Bischoff (2008) and Rout et al. (2009) discovered a high abundance of such objects in unequilibrated clasts from NWA 753. They determined that the abundance of CAIs in R chondrites is less than it is in carbonaceous chondrites, but greater than in ordinary and enstatiteA mineral that is composed of Mg-rich pyroxene, MgSiO3. It is the magnesium endmember of the pyroxene silicate mineral series - enstatite (MgSiO3) to ferrosilite (FeSiO3). Click on Term to Read More chondrites. These CAIs in R chondrites are significantly smaller than those in CM and CV chondritesMeteorite class named after the Vigarano meteorite that fell in Italy in 1910. They have abundant large, well-defined rimless (?) chondrules of magnesium-rich olivine (~0.7 mm diameter; 40-65 vol. %), often surrounded by iron sulfide. They also contain 7-20 vol. % CAIs. The often dark-gray matrix is dominated by Fe-rich Click on Term to Read More, but similar in size to those in CH, O, and E chondrites. Based on Δ17O values, the CAIs in R chondrites were divided into 16O-rich (~ –23‰ to –26‰), 16O-depleted (~ –2‰), and heterogeneous (–25‰ to +5‰). As with CAIs of other chondrite groups, R chondrite CAIs were likely formed in an 16O-rich nebular region, with some sustaining subsequent isotopic exchange with an 16O-depleted nebular gas or through metasomatism on the parent asteroid. Taking into account the differences in mineralogy between the majority of R chondrite CAIs and those from other groups, R chondrites contain a unique subset of CAIs. That said, the investigators argue that certain types of CAIs present in R chondrites strongly resemble some of those found in the CO-chondrite group, especially those present in the more highly metamorphosed meteorites like Ornans, Moss, Isna, and Lancé. Other Al-rich objects in R chondrites share similarities to those from the O- and E-chondriteType of meteorite high in the mineral enstatite and also referred to as E-chondrites. Although they contain substantial amounts of Fe, it is in the form of Ni-Fe metal or sulfide rather than as oxides in silicates. Their highly reduced nature indicates that they formed in an area of the Click on Term to Read More groups.
Kita et al. (2013) employed the same technique for NWA 753 that is applied to ordinary chondriteWork in Progress Ordinary chondrites (OCs) are the largest meteorite clan, comprising approximately 87% of the global collection and 78% of all falls (Meteoritical Society database 2018)1. Meteorites & the Early Solar System: page 581 section 6.1 OC of type 5 or 6 with an apparent shock stage of S1, Click on Term to Read MorechondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More for determination of the petrologic subtype from 3.00 to 3.2, which is based on the alteration resistant Cr content in ferroan 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 (Grossman, 2004; Grossman and Brearley, 2005). They determined that the corresponding petrologic subtype for the least equilibrated material in NWA 753 is 3.15–3.20, the lowest subtype found among R chondrites. Crowther et al. (2015) utilized I–Xe chronometry in a preliminary study of four samples of NWA 753 having a petrologic typeMeasure of the degree of aqueous alteration (Types 1 and 2) and thermal metamorphism (Types 3-6) experienced by a chondritic meteorite. Type 3 chondrites are further subdivided into 3.0 through 3.9 subtypes. range of 3.15–3.9. They found that a correlation exists between the closure age and the petrologic type of a sample, with a younger age being correlated with a higher degree of metamorphism. This range of petrologic types reflects a difference in age of ~5 m.y. years and is consistent with cooling within an onion-shell structure on the R-chondrite 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.
Consistent with the absence of solar gases, NWA 753 is not thought to have been part of a 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). Click on Term to Read More for any significant length of time. Evidence gathered thus far indicates that NWA 753 experienced a relatively rapid transfer from the 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 to the Earth, having a 21Ne-based CRE age of 12.8 m.y. (Schultz et al., 2005). Subsequent noble gasElement occurring in the right-most column of the periodic table; also called "inert" gases. In these gases, the outer electron shell is completely filled, making them very unreactive. Click on Term to Read More analyses of the known Northwest Africa R chondrites were conducted by Vogel et al. (2014). Their ~16 groupings vary slightly from the previous pairings suggested by other investigators, and they propose an ~14 m.y. CRE age group representing possible common source craters and/or 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 events which includes R chondrites with the NWA series designations 753, 1472, 1476, 1477, 1478, 1566, 4360, 4419, and 5606.
This unique chondrite group was originally named for the Carlisle Lakes, Australia (49.5 g) specimen, but has since been renamed for the only fall of the group from Rumuruti, Kenya (67 g) in 1934. Two views of a 0.54 g partial slice of NWA 753 are shown above: the right photo shows the melted fusion-crusted surface, while the left photo shows the abundant tiny chondrules characteristic of this chondrite group.
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