Pillistfer

EL6
(ELa6 in Weyrauch et al., 2018)

Fell August 8, 1868
58° 40′ N., 25° 44′ E. At 12:30 P.M. in Estonian SSR, sonic booms were heard and stones fell at Aukoma, Kurla, Wahhe, and Sawiauk. The weight of these stones was ~14 kg, 7.5 kg, 1.5 kg, and 0.25 kg. These falls are also known by the names of Pilistvere and Pillistvere.

Weyrauch et al. (2018) analyzed the 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 and chemical data from 80 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). 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 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 troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites. and the Fe concentration in niningerite and alabanditeMagnesium sulfide found in aubrites and EL chondrites. Its formula is MnS. (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 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 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 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 metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. 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 Pillistfer is a member of the ELa subgroup.

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, Pillistfer has geothermometers that indicate a classification of EL6β.

Enstatite chondrites were formed in a highly 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 environment. Therefore, they contain virtually no 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 in the oxide form—much less by comparison to other chondrites and to the terrestrial planetsRocky planets: Mercury, Venus, Earth, and Mars. These planets have physical characteristics, chemical composition and internal structure similar to the Earth. The terrestrial planets have 0.4% of the total mass of all the planets in the Solar System. Some large satellites of planets are also similar to the characteristics of. Iron in EL6 chondrites is depleted and isotopically fractionated compared to less metamorphosed EL3 and EH chondrites (Wang et al., 2013). A 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 analysis utilizing nonmagnetic micron-scale grains from Pillistfer was conducted by Lavrentjeva and Lyul (2017). They found depletions in siderophile elements and enrichments in lithophile elements, which indicates that nebular metal–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 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. of precursor material occurred, as well as redistribution during 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. metamorphism. The mineral sinoite (silicon oxynitride) has been found to occur in Pillistfer and many other EL chondrites that have a high bulk N content. Sinoite is associated with crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. from an impact melt, or alternatively, with metamorphic processes. This suggests that Pillistfer experienced a period of high, possibly melt-forming temperatures. A rapid cooling phase was initiated consistent with 0.8°C/day (Kissin, 1989). This was followed by a period of annealing and then a final shock to stage S2.

An isochron age for Pillistfer representing the K–Ar systemDefinable part of the universe that can be open, closed, or isolated. An open system exchanges both matter and energy with its surroundings. A closed system can only exchange energy with its surroundings; it has walls through which heat can pass. An isolated system cannot exchange energy or matter with closure was calculated by Bogard et al. (2010) to be 4,541 (±7) m.y. ago., a similar age to that of several equilibrated E chondrites. A comparison of the younger Ar–Ar ages measured for ordinary chondrites suggests that E chondrites cooled more quickly, possibly reflecting a smaller parent body size, a lower initial heating level, a shallower burial, and/or a collisional disruption prior to K–Ar closure. More recently, employing a broader range of EL chondrite petrologic types (i.e., formation temperatures), Hopp et al. (2013, 2014) determined a lower corrected age range for metamorphic cooling of EL5 and EL6 meteorites of 4.48–4.51 b.y. In a similar manner, the Ar–Ar isochron age for an EL3 chondrite reflected a younger age, possibly representing a late-stage impact ~4.43–4.47 b.y. ago. This better constrained age range would allow for a more extended period of time for parent body cooling and a relaxation of the constraints on the parent body size. However, since the K–Ar closure for the EL parent body occurred 30 m.y. earlier than that of the H-chondrite parent body, the size of the EL parent body was most likely significantly smaller than the H parent body.

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 isotopic studies place the formation of enstatite chondrites on the terrestrial fractionation line, which is taken by some to mean that they formed within the inner Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids.. Based on 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. systematics and its correlation with 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. distance, Shukolyukov and Lugmair (2004) concluded that E chondrites originated ~1.0–1.4 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 from 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 before being perturbed into their present locations in 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. Similarly, Nakashima et al. (2006) calculated a heliocentric distance of >1.1 and 1.3 AU for two EL3 chondrites (ALH 85119 and MAC 88136, respectively) 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. concentrations.

In contrast, the identification of the E-asteroid group, including Hungaria at 1.94 AU, Nysa at 2.42 AU, and Angelina at 2.68 AU, suggests that the actual solar region of formation could lie at a greater heliocentric distance. Cosmochemists are presently trying to construct a suitable theory involving oxygen depletion in this E-asteroid region of the Solar System to explain the conflicting theories. The specimen pictured above is a 5.7 g partial slice showing the abundant free metal that characterizes this group.