Krymka

LL3.2


Fell January 21, 1946
47° 50′ N., 30° 46′ E. Following a shower of stones that fell over the Nicholayev region of the Ukraine, USSR, about 50 kg of stones were collected; they turned out to be one of the most primitive ordinary 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 ever discovered. This is a highly unequilibrated chondriteA chondrite with heterogeneous mineral compositions (e.g., olivine grains with differing FeO/(FeO+MgO) ratios., poor in both metallic and 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 Fe. Due to the widely varying results obtained when utilizing the ratio of metallic to total Fe for distinguishing between an L3 and LL3 classification, less ambiguous criteria were employed (total Fe/Mg and Ni/Mg ratios, and Fe–S relationships) to establish a classification for Krymka of LL3. Early analyses of Krymka based on texture, TL sensitivity, highly volatileSubstances which have a tendency to enter the gas phase relatively easily (by evaporation, addition of heat, etc.). 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 content, and 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 heterogeneity, were consistent with a sub-classification of LL3.0. However, subsequent studies led to its re-classification as LL3.1, consistent with a very mild metamorphicRocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. history and retention of primary features.

Most recently, a new decimal scheme which is more discriminating at the lowest petrologic types associated with highly unequlibrated chondrites (3.0–3.1–3.2) was proposed by J. Grossman (2004), and J. Grossman and A. Brearley (2005). The new classification scheme, based on a sensitive analytical technique utilizing the variation in the distribution of Cr 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, is virtually unaffected by the processes of terrestrial weathering and aqueous alteration. The scale of the new decimal 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 has been extended as follows:

3.00–3.05–3.10–3.15–3.2

They have identified several additional parameters, which, when used in combination, are instrumental in determining an accurate classification at the lowest petrologic grades:

At the onset of thermal metamorphism, 1) Cr is exsolved from ferroan olivine forming fine Cr-rich precipitates, which, with progressive metamorphism, become coarser within the olivine cores and form rims on the olivine surfaces; 2) very fine-grained FeS grains in chondruleRoughly 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 rims and in fine-grained matrixFine grained primary and silicate-rich material in chondrites that surrounds chondrules, refractory inclusions (like CAIs), breccia clasts and other constituents. become coarser, and secondary sulfides form within 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; 3) Fe and Mg in olivine are homogenized and 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 grains are equilibrated; 4) abundances of presolar grainsMineral grains that formed before our solar system. These tiny crystalline grains are typically found in the fine-grained matrix of chondritic (primitive) meteorites. Most grains probably formed in supernovae or the stellar outflows of red giant (AGB) stars before being incorporated in the molecular cloud from which the solar system are diminished; 5) Na and other alkalis are initially lost from the matrix and enter type-I chondrules, causing zonation, only to reverse direction with progressive metamorphism; 6) albite crystallizes from type-II chondrules causing blue CL and increased TL sensitivity.

In subsequent studies of chromiteBrownish-black oxide of chromium and iron (Cr-Fe oxide), Cr2FeO4, found in many meteorite groups. zoning profiles along with the chromite content of individual ferroan olivine grains, Grossman (2008) was able to further resolve the 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. for chondrites at the lowest metamorphic stages. These two petrographic features provide a reference for a sequencial history of increasing thermal metamorphism that is consistent among olivine grains within each 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. For metamorphic types 3.00–3.03, chromite zoning profiles are smooth and correlate with igneous FeO zoning profiles. In addition, at this lowest metamorphic stage chromite contents account for 0.3–0.5 wt% in the 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 studied. While chromite contents in type 3.05–3.10 chondrites still reflect the lowest degrees of metamorphism, chromite now exhibits igneous zoning profiles which are no longer smooth. Upon reaching a degree of metamorphism equivalent to type 3.15, chromite zoning has diminished considerably, and chromite abundance is now only 0.1–0.2 wt%. With metamorphic types of at least 3.2, no zoning is observed and chromite abundance is mostly less than 0.1 wt%.

Based on details of this new scheme, Krymka was found to have a low Cr content in olivine, a diminished abundance of presolar grains with no Xe–P3 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. release, and other characteristics most consistent with a petrologic type 3.2. In a study by Bonal et al. (2006), utilizing Raman spectroscopyTechnique of splitting electromagnetic radiation (light) into its constituent wavelengths (a spectrum), in much the same way as a prism splits light into a rainbow of colors. Spectra are not smooth but punctuated by 'lines' of absorption or emission caused by interaction with matter. The energy levels of electrons in and other petrologic tracers (i.e., noble gas content, presolar grain abundance, and zoning of olivine phenocrysts), all results supported a petrologic type of 3.2 for Krymka.

An intense shock event corresponding to pressures of at least 30 GPa is recorded in mm- to cm-sized melt pockets in Krymka, reflecting closed system behavior of an in situ melting event. Temperatures reached ~1500°C in the melt zones producing igneous textures, which was followed by a high cooling rate, greater than 100°C/hour, resulting in non-equilibrium crystallizationPhysical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. (Semenenko and Perron, 2005). Metal–troiliteBrass colored non-magnetic mineral of iron sulfide, FeS, found in a variety of meteorites. intergrowths were formed, with chromite and Fe–Na phosphate glass crystallizing within troilite. Following crystallization, a less intense shock caused 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 deformation features. In a separate study of two LL chondrites, NWA 1701 and LAR 06298, Weirich et al. (2009) determined an Ar–Ar age of ~1 b.y., possibly reflecting the last major impact on the LL chondriteOrdinary chondrites ("low Fe" / "low metal") with only 1 to 3% free metal. Their olivine is more Fe-rich than in the other ordinary chondrites (Fa27-32), implying that the LL types must have formed under more oxidizing conditions than their H or L cousins. Orthopyroxene compositions are also Fe-the rich 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..

Fayalitic olivine of heterogeneous composition is the most common matrix component. It occurs in several morphologies, and can be found as fine-grained rims on chondrules and lithic clasts. It is thought to represent a primary condensateIn the solar nebula, product of a chemical condensation reaction where a mineral phase precipitates (condenses) directly from a cooling vapor. derived from the vaporization and recondensation of olivine-rich dust in an 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 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 (Weisberg et al., 1997). This fayalitic olivine was then accreted and incorporated into the Krymka parent body, and thereafter it experienced repeated episodes of lithification and fragmentation. The clastic matrix of Krymka comprises many diverse mineral and lithic components, including various silicates, oxides, and metals. In addition, xenoliths of Kakangari-like chondrite material have been observed (Funk et al., 2011). Metzler and Chaussidon (2014) identified a lithic clastA mineral or rock fragment embedded in another rock. in the Krymka meteorite that consists of an assemblage of plastically deformed chondrules; this type of clast was termed a ‘cluster chondrite clast’. Utilizing Al systematics, the crystallization age of several chondrules from this clast was determined to be 0.44 (±0.18) m.y. after CAISub-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 formation (one chondrule might be slightly older still). It was conjectured that this data represents the earliest known crystallization of chondrules in Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids. history, and could mark the earliest stage of accretionAccumulation of smaller objects into progressively larger bodies in the solar nebula leading to the eventual formation of asteroids, planetesimals and planets. The earliest accretion of the smallest particles was due to Van der Waals and electromagnetic forces. Further accretion continued by relatively low-velocity collisions of smaller bodies in the of this chondrite parent body.

Metal occurs in chondrule interiors and rims, as well as in the matrix. The metal in chondrule interiors and matrix is mostly spheroidal and Cr-rich, and is located between olivine grains. Large (0.2–1.0 mm), rimmed (an inner silicate and an outer sulfide layer), metal-sulfide nodules occur in the matrix. In those cases where the metal nodules contain Si and Cr, the associated sulfide contains inclusions of Si, Cr, and Ca. In addition, sulfide–metal–phosphate assemblages incorporating merrillite and chlorapatite are present. These phosphates were formed in a multi-stage process, initially involving the exsolutionSegregation, during cooling, of a homogeneous solid solution into two or more different solids. of schreibersiteNi-Fe phosphide mineral, (Fe,Ni)3P, yellowish in color and predominantly found in iron and stony-iron meteorites. Schreibersite can also be found in a variety of other meteorites including some acapulcoites, aubrites, enstatite chondrites and achondrites, lunars, ureilites, winonaites and a smattering of other meteorite types like CM, CO and CB. Schreibersite from FeNi-metal. This was followed by sulfidation of schreibersite by nebular hydrogen-sulfide gas to produce sulfide–metal–schreibersite assemblages, and finally, 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 and reaction with Ca and Cl derived from matrix silicates. These metal nodules appear to be primary nebular condensates, with a Co 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 content that plots within the LL group range.

Notably, porous, dusty spherules, which are primarily composed of fine-grained, cryptocrystallineCrypto meaning "hidden" refers to a rock texture in which individual crystals are too small to be distinguished even using a standard petrographic microscope. Crystals are typically less than a few μm in size - any smaller and the texture would be considered amorphous. Among sedimentary terrestrial rocks, chert and silicate dust, and which are rimmed by sub-µm- to µm-sized sulfide and metal grains, were identified within dark lithic fragments in Krymka (Semenenko and Girich, 1999). These porous spherules are thought to represent chondrule precursors that formed by direct accretion of fine-grained nebular dust onto coarse-grained nuclei. A large abundance of tiny CAI components were also found within a dark lithic fragment (Semenenko et al., 2001).

In another study, a rare olivine microchondrule-bearing clast was identified within a lithic fragment in Krymka (Rubin,1989). It is composed of 0.003–0.031 mm-sized or less, BO and G chondrules, embedded within a recrystallized silicate matrix incorporating tiny sub-µm-sized FeNi grains. The microchondrules, which are zoned in FeO (increasing from 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. to rim), are found among Mg-rich constituents within the clast, indicating that oxidation occurred before accretion.

Additional exotic components were accreted during the formation of the Krymka host, including rare black carbonaceous xenoliths, commonly referred to as ‘mysterite’. This material is enriched in volatile siderophiles such as Ag, Tl, Zn, and Bi, and represents a late condensate from a metal-depleted region of the solar nebulaThe primitive gas and dust cloud around the Sun from which planetary materials formed., possibly related to cometary material (Campins and Swindle, 1998). These xenoliths contain abundant troilite in the matrix and they lack evidence of relict chondrules. They also contain graphiteOpaque form of carbon (C) found in some iron and ordinary chondrites and in ureilite meteorites. Each C atom is bonded to three others in a plane composed of fused hexagonal rings, just like those in aromatic hydrocarbons. The two known forms of graphite, α (hexagonal) and β (rhombohedral), have microcrystals, considered to be a metamorphic product from organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes. compounds, which are distributed between silicate grains (Semenenko, 1996). The metamorphic temperature is constrained at ~300°C and ~500°C (Weber et al., 2006). Evidence of shock meltingComplete melting of target material produced by the shock of a meteoric impact. Different minerals will experience certain shock effects at different pressures and temperatures. For example, dense target rocks like anorthosite will typically experience whole rock melting above 50 to 60 GPa, while chondritic rocks require more than 70 is manifest in the alteration effects of the rim and matrix.

Another exotic component is the fine-grained, graphite-bearing fragments that may share a common organic-based precursor with the black carbonaceous xenoliths. These graphite-bearing fragments are friable, fine-grained objects with recrystallized textures, containing carbonElement commonly found in meteorites, it occurs in several structural forms (polymorphs). All polymorphs are shown to the left with * indicating that it been found in meteorites and impact structures: a. diamond*; b. graphite*; c. lonsdalite*; d. buckminsterfullerene* (C60); e. C540; f. C70; g. amorphous carbon; h. carbon nanotube*. in the form of organic compounds, C-rich material, and graphite (Semenenko et al., 2005). The morphologically unique graphite crystals in these xenolithic fragments were formed either by shock metamorphismMetamorphism produced by hypervelocity impact between objects of substantial size moving at cosmic velocity (at least several kilometers per second). Kinetic energy is converted into seismic and heat energy almost instantaneously, yielding pressures and temperatures far in excess those in normal terrestrial metamorphism. On planetary bodies with no atmosphere, smaller of C-bearing material on the Krymka parent body, or by metamorphism on the primary carbonaceous parent body (Semenenko et al., 2004, 2005). Like the carbonaceous xenoliths, these fragments represent previously unknown unequilibrated carbonaceous material which contains a high abundance of troilite within the silicate mesostasisLast material to crystallize/solidify from a melt. Mesostasis can be found in both chondrules, in the matrix around chondrules, and in achondrites as interstitial fine-grained material such as plagioclase, and/or as glass between crystalline minerals.  , and which contains a low abundance of relict chondrules. Interestingly, these exotic fragments have O-isotope ratios and other chemical and isotopic values that are similar to the graphite in CR chondrites.

Other noteworthy xenolithic material has been documented from Krymka. Small, pre-accretionary, fine-grained, C-rich clasts are scattered throughout this meteorite, possibly having a distant relationship to the graphite-bearing and carbonaceous inclusions. Furthermore, some C-rich material has been mobilized by shock to form irregular areas and veins that penetrate into cracks and boundaries of silicate and feldspathic grains. A zoned macrochondrule was studied that consists of two metal–troilite mantles with irregular graphite grains (crystallized during igneous processes), along with a fine-grained rim containing regular graphite crystals (formed by shock metamorphism) (Semenenko and Girich, 2011). This macrochondrule was likely formed by flash melting of a huge silicate precursor dust aggregate containing metal–troilite and organic compounds.

Most recently, dark, porous clasts containing magnetiteFe oxide, FeFe2O4, containing oxidized iron (Fe) found in the matrix of carbonaceous chondrites and as diagnostic component in CK chondrites. In CK chondrites, magnetite is typically chromian, containing several wt. % Cr2O3. spherules and framboids have been identified (Girich and Semenenko, 2001). These clasts exhibit chemical and mineralogical similarities to the CI chondrites, and may represent precursor material from that carbonaceous group. Another fine-grained, dark xenolithFragment of a rock or meteorite that formed apart from the host material. that was identified contains rare chondrules and FeNi-metal, and has a composition and a SiO/MgO ratio which suggests that it may be a primitive precursor of H chondriteOrdinary chondrites with a high content of free Ni-Fe metal (15-19 vol. %) and attracted easily to a magnet. Their main minerals are olivine (Fa16-20) and the orthopyroxene bronzite (Fs14.5-18.5), earning them their older name of bronzite chondrites. Chondrules average ~0.3 mm in diameter. Comparison of the reflectance spectra of material (Semenenko and Girich, 2005).

Also present are presolar nanodiamonds that contain a new high-temperature Xe phase. Xenon isotopeOne of two or more atoms with the same atomic number (Z), but different mass (A). For example, hydrogen has three isotopes: H, H (deuterium), and H (tritium). Different isotopes of a given element have different numbers of neutrons in the nucleus. data suggest that Krymka was irradiated within 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).   on a large parent body at a significant shielding depth. CorundumCrystalline form of aluminium oxide, Al2O3, found in Ca-Al-rich inclusions (CAIs). Corundum-bearing  CAI are a rare class of high-temperature condensates from the inner regions of the protoplanetary disk. grains constituting ~5 ppmParts per million (10). have also been identified within the matrix (Strebel et al., 2000); however, none of them exhibit an anomalous presolar signature. On the other hand, one presolar spinelMg-Al oxide, MgAl2O4, found in CAIs. grain identified in a combined residue of Krymka, Semarkona, and Bishunpur has anomalous isotopic compositions of Mg, O, and Al—all consistent with an origin in an intermediate-mass AGB starStars on the Asymptotic Giant Branch, which represents a late stage of stellar evolution that all stars with initial masses < 8 Msun go through. At this late stage of stellar evolution, gas and dust are lifted off the stellar surface by massive winds that transfer material to the interstellar of ~5 M_⊙ (Lugaro et al., 2007).

In a study by Tomomura et al. (2004), the Si/Mg-derived formation ages of ferromagnesian chondrules from Krymka were measured. The results indicate that chondrules were formed continuously from 1.4 to 2.6 m.y. after CAI formation, with a peak at 1.9–2.0 m.y. Two views of a 4.5 g slice of Krymka are shown above—photography is courtesy of S. Vasiliev.