Saint Sauveur

EH5
Impact-melt 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
(EHb5 in Weyrauch et al., 2018)

Fell July 10, 1914
43° 44′ N., 1° 23′ E. Around 2:00 on a July afternoon, people in Haute Garonne, France heard detonations and observed the 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 of a meteorHow long Sonic booms Of the several 10s of tons of cosmic material entering Earth's atmosphere each day, only about one ton reaches the surface. An object's chance of survival depends on its initial mass, speed and angle of entry, and friability (tendency to break up). Micrometeoroids radiate heat so Click on Term to Read More. 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 weighing ~14 kg was recovered 1.5 km south of Saint-Sauveur. The owner of the field in which it fell, Antoine Esculie, donated the stone free of charge to the Museum of Toulouse (R. Mathieu).
Photo courtesy of Société d’Histoire Naturelle de Toulouse
Originally published in the Bulletin de la Société d’Histoire Naturelle de Toulouse, vol. 93 (1958), by G. Astre.
Pictured L–R: Gaston Astre, geologist and naturalist, director of the Museum of Toulouse (1944–1962); Guillaume Champagne, priest of Saint-Sauveur; unidentified neighbor; Barthélémy Cazemajou, mayor of Saint-Sauveur Saint-Sauveur is a member of the high-Fe group of 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 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, one of a very small number classified as 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. 5. It is considered to be an impact-melt breccia, and has been weakly shock metamorphosed to stage S3 corresponding to a shock pressure of ~10 GPa. Shock features include planar fractures and twinned clinoenstatite lamellae within 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, and the occurrence of opaque veins of kamaciteMore common than taenite, both taenite and kamacite are Ni-Fe alloys found in iron meteorites. Kamacite, α-(Fe,Ni), contains 4-7.5 wt% Ni, and forms large body-centered cubic crystals that appear like broad bands or beam-like structures on the etched surface of a meteorite; its name is derived from the Greek word Click on Term to Read More and troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites. Click on Term to Read More.

Enstatite chondrites are the most reducedOxidation 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 meteorites among chondrites as evidenced by their extremely low FeO content, and by the presence of rare sulfide minerals such as oldhamiteMn-Ca sulfide, (Mn,Ca)S, is a pale to dark brown accessory mineral found in minor amounts in highly reduced meteorites such as many enstatite chondrites, and some aubrites and enstatite achondrites. Oldhamite in enstatite chondrites likely formed by solar nebular gas condensation. CaS Oldhamite was also found in the most fresh Click on Term to Read More, daubréelite, and alabanditeMagnesium sulfide found in aubrites and EL chondrites. Its formula is MnS. Click on Term to Read More (EL) or niningerite (EH). Moreover, 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 occurs primarily as low-Ni kamacite in both the EH and the EL groups. Surprisingly, it has been demonstrated by Macke et al. (2009) that these two groups do not actually differ in their iron content, and that they are indistinguishable in densityMass of an object divided by its volume. Density is a characteristic property of a substance (rock vs. ice, e.g.). Some substances (like gases) are easily compressible and have different densities depending on how much pressure is exerted upon them. The Sun is composed of compressible gases and is much Click on Term to Read More, porosityThe volume percentage of a rock that consists of void space. Vesicular porosity is a type of porosity resulting from the presence of vesicles, or gas bubbles, in igneous rock such as the pumice presented here. Vesicular porosity is very rare in meteorites and is often associated with slag, one Click on Term to Read More, and magnetic susceptibility as well; however, differences in siderophile, chalcophile, and other mineralogical abundances can be employed to distinguish the two groups. The EH and EL groups are clearly resolved from each other based on compositional, textural, and mineralogical differences, as well as by O-isotopic data and formation intervals, indicating that they were derived from separate, but closely related parent bodies. In addition, both Fe- and Zn-isotopic compositions are fractionated to different degrees between EL and EH chondrites; EL chondrites are heavier than EH chondrites, indicating that EL chondrites experienced higher volatilization due to its formation closer to the SunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the (Mullane et al., 2005), or alternatively, due to elemental fractionationConcentration or separation of one mineral, element, or isotope from an initially homogeneous system. Fractionation can occur as a mass-dependent or mass-independent process. Click on Term to Read More during impact shock events (Rubin et al., 2009). The nonrefractory siderophile, chalcophile, and alkali elements in Saint-Sauveur clearly establish it as a member of the EH group.

Within the EH group, a distinction can be readily made between EH3 and EH4,5 petrologic types based on 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 compositions. One difference is evident in their respective Ni content in kamacite (EH3: 24–33 mg/g Ni; EH4,5: 65–79 mg/g Ni), which might be explained by the depletion of Ni by the formation of high-Ni perryite at the surface of kamacite grains in the EH3 chondrites. Perryite formation was induced through hot nebular exchange reactions in which metal was converted to FeS, thus freeing up Ni to form perryite. In contrast to the unmetamorphosed E chondrites, this mineral did not survive subsequent metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. Click on Term to Read More heating in E chondrites of higher petrologic types. Since elemental abundances in E chondrites of petrologic types 4 and 5 are practically the same, it is only from observations of mineralogical changes, produced by varying degrees of thermal metamorphism, that a distinction can be made between them.

The Van Schmus–Wood (1967) scheme for petrographic type has been modified for enstatite chondrites, establishing both a textural type (3–7), reflecting peak metamorphic temperature, and a mineralogical type (α–δ), pertaining to the cooling history (Zhang and Sears, 1996; Quirico et al., 2011). Under this classification scheme, Saint-Sauveur has thermometers that give it a classification of EH5γ.

The possibility that the EH group is comprised of two distinct subgroups has been considered. Within these two subgroups the cooling rate and MnS content in niningerite are correlated. This correlation is not adequately explained by burial depth or impact-generated differences, and therefore, formation on two separate bodies has been suggested by some. The thermal history of Saint-Sauveur is consistent with inclusionFragment of foreign (xeno-) material enclosed within the primary matrix of a rock or meteorite. Click on Term to Read More in the subgroup that experienced fast cooling with a low MnS content in niningerite. Weyrauch et al. (2018) analyzed the mineral and chemical data from 80 enstatite chondrites representing both EH and EL groups and spanning the full range of petrologic types for each group. They found that a bimodality exists in each of these groups with respect to both the Cr content in troilite and the Fe concentration in niningerite and alabandite (endmembers of the [Mn,Mg,Fe] solid solutionCompositional variation resulting from the substitution of one ion or ionic compound for another ion or ionic compound in an isostructural material. This results in a mineral structure with specific atomic sites occupied by two or more ions or ionic groups in variable proportions. Solid solutions can be complete (with series present in EH and EL groups, respectively). In addition, both the presence or absence of daubréelite and the content of Ni in kamacite were demonstrated to be consistent factors for the resolution of four distinct E 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 groups: EHa, EHb, ELa, and ELb (see table below).

A few other E chondrites with intermediate mineralogy have also been identified, including LAP 031220 (EH4), QUE 94204 (EH7), Y-793225 (E-an), LEW 87223 (E-an), and PCA 91020 (possibly related to LEW 87223). Studies have determined that these meteorites were not derived from the EH or EL source through any metamorphic processes, and some or all of them could represent separate E chondrite asteroids. The revised E chondrite classification scheme of Weyrauch et al. (2018) including selected examples from their 80-sample study can be found here. It was determined that Saint-Sauveur is a member of the EHb subgroup.

Enstatite chondrites have O-isotope compositions that plot along the terrestrial fractionation line, suggesting that they may have formed within the Mercury–Venus region in the inner Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids., and that they were subsequently perturbed into the inner regions of 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. In such a case, the strongly 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 Click on Term to Read More conditions under which they were formed could have been promoted by an excess of H and C, maintained by a hot, dusty environment close to the Sun. Utilizing Mn–Cr 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 systematics, Shukolyukov and Lugmair (2004) concluded that the E chondrites formed at a location closer to the Sun—between at least 1 AUThe astronomical unit for length is described as the "mean" distance (average of aphelion and perihelion distances) between the Earth and the Sun. Though most references state the value for 1 AU to be approximately 150 million kilometers, the currently accepted precise value for the AU is 149,597,870.66 km. The Click on Term to Read More outward to 1.4 AU—than at the location within the asteroid belt they now occupy.

However, if the region between ~1.0 and 1.4 AU were truly the formation location of E chondrites, they should have highly elliptical orbits; but this is not what is observed. In fact, reflectance spectrometry has identified asteroids similar to E chondrites in stable orbits between 1.8 and 3.2 AU, suggesting that the inner asteroid belt is the actual location where they originated. In addition, a 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 distance of ~2.0–2.9 AU was calculated for two E chondrites on the basis of their implanted solar 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 concentrations (Nakashima et al., 2004). Furthermore, an isotopically anomalous Xe-containing component, associated with an anomalous light N component, is found proportionately in both carbonaceous and enstatite chondrites, but not on Earth. Since this component is almost certainly of nucleosynthetic origin, it follows that the carbonaceous and enstatite chondrites should share a similar heliocentric formation location. In this case, the strongly reducing conditions under which E chondrites formed could have been promoted by the loss of refractory oxides prior to condensation from the local 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.

Data from Rb–Sr systematics infer a formation age for Saint-Sauveur of 4.516 (±0.029) b.y., with indications of a high-temperature shock event occurring 60–200 m.y. after formation, consistent with the presence of the high-pressure silicaSilicon dioxide, SiO2. polymorph cristobaliteHigh temperature polymorph of silicon dioxide (SiO2). Has the same chemical composition as coesite, stishovite, seifertite and tridymite but possesses a different crystal structure. This silica group mineral occurs in terrestrial volcanic rocks, martian and lunar meteorites, chondrites and impact glasses like Libyan Desert Glass. Cristobalite has a very open Click on Term to Read More. This cristobalite was preserved through rapid cooling (Kimura et al., 2005). The occurrence in Saint-Sauveur of the mineral keilite, produced from melting of niningerite and troilite, is also indicative of an impact melting event accompanied by rapid quenching (Hill et al., 2014). The presence of fluor-richterite grains also attests to an impact-melt history. Cosmic-ray exposure ages are generally lower for EH chondrites than for EL chondrites, 0.5–7 m.y. and 4–18 m.y., respectively. More in-depth information on the complex thermal history of the EH chondrites can be found on the Sahara 97096 page.

A xenolithFragment of a rock or meteorite that formed apart from the host material. Click on Term to Read More that was found in the carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than Click on Term to Read More Kaidun, named Kaidun III, has been determined to be an EH5 inclusion, one that underwent hydrationReaction of a substance with water. Click on Term to Read More on the Kaidun 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. Interestingly, another clastA mineral or rock fragment embedded in another rock. Click on Term to Read More found in a Kaidun sample is a rare EL3, named Kaidun IV. In addition to three Antarctic EH5 members, the St. Mark’s meteorite is the only other non-Antarctic EH5 sample in our collections. The specimen of Saint-Sauveur shown above is a 1.34 g partial slice obtained in a trade with the Muséum National d’Histoire Naturelle, Paris, France, by International Meteorite Brokerage. The photo below is the 14 kg 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 of Saint-Sauveur in the Muséum de Toulouse.
click on photo for a magnified view
Photo courtesy of Didier Descouens—Muséum de Toulouse