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Knyahinya

L/LL5
standby for knyahinya photo
Fell June 9, 1866
48° 54′ N., 22° 24′ E. Following detonations, a shower of stones numbering more than 1000, and weighing ~500 kg, fell at 5:00 P.M. in the Ukraine, USSR. A strewnfield with dimensions of 2 × 0.75 miles was delineated. The nearly spherical mass of Knyahinya had an estimated pre-atmospheric diameter of 90 cm, corresponding to a mass of ~1,300–1,400 kg, before it was broken into two nearly symmetrical sections upon impact; the largest section weighed 293 kg. The CRE age of Knyahinya as inferred from cosmic-ray track data and cosmogenic Ne ratios is 38 m.y. Knyahinya has proven to be instrumental in studies of cosmogenic nuclide production systematics due to its simple single-stage exposure history and its simple shielding geometry, allowing exact depth profiles to be determined.

Although Knyahinya has an accepted classification of L5 based on its trace element composition, it is partially resolved into an intermediate L/LL chondrite group based on studies involving the Co abundance in matrix kamacite and on its bulk metallic iron content similar to that of an LL chondrite. Contrariwise, the Ir/Au atomic ratio of Knyahinya falls within the H range (3.4–3.8) rather than the LL–L range (2.6–3.5).

It was demonstrated by Szurgot (2016) that the mean atomic weight (Amean) of meteorites can be used to resolve the OC groups, including the intermediate groups L/LL and H/L. Amean values can also be predicted through various equations based on other parameters such as atomic Fe/Si ratio, grain density, and magnetic susceptibility, and these Amean values all consistently resolve these groups into the ordered sequence LL < L/LL < L < H/L < H. Knyahinya has Amean values of 23.24 (chemical composition), 23.21 (Fe/Si atomic ratio), and 23.54 (grain density). Furthermore, it was demonstrated that Amean values are lower for unequilibrated type 3 samples than for equilibrated samples within each OC group due to the presence of water; Amean values for petrologic types 4–6 are indistinguishable within each group. standby for amean diagram
Diagram credit: M. Szurgot, 47th LPSC, #2180 (2016)
Amean based on chemical composition (Eq. 1), Fe/Si atomic ratio (Eq. 2), and grain density (Eq. 3) Members of the L/LL chondrite group include L/LL3 Esperance, L/LL4 Seemore Downs, Bjurböle, and Cynthiana, L/LL5/6 Sahara 97021, and L/LL6 Acfer 041, as well as the partially resolved L/LL3 Inman and L/LL6 Holbrook. In a study of the shock stage of Knyahinya conducted by Fürj et al. (2009), mosaicism in olivines and twinning in pyroxenes were detected consistent with a shock stage of S4. The specimen of Knyahinya shown above is a 1.93 g partial slice. The photo below shows a print depicting the Knyahinya fireball—from a book published in Denmark a few years after the fall (click image for title page). [A description posted online: ‘Mr. Kolbay’s drawings of what he and Mr. Rainer saw from near Eperies (today Pre šov, Slovakia), ~92 km from the Knyahinya strewnfield, as presented by W. R. v. Haidinger in 1866.’]

standby for title page photo
Photo courtesy of Lars Pedersen


The largest mass of Knyahinya weighs 293 kg, which is curated at the Natural History Museum, Vienna.


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Tieschitz

H/L3.6
standby for tieschitz photo
Fell July 15, 1878
49° 36′ N., 17° 7′ E. A single 27.4 kg stone was seen and heard to fall at 1:45 in the afternoon in Prostejov, Jihomoravsky, Czechoslovakia. Analysis was conducted at the Museum of the Technical High School of Brünn, and Tieschitz was classified as an unbrecciated, unequilibrated ordinary chondrite with a shock stage of S1/S2. This meteorite has preserved the early record of large-grained, pristine chondrites.

Tieschitz does not follow the ordinary chondrite metal–silicate trends in that it has an anomalous Fe content intermediate between the H and L groups, and it has a lower K content than is typical for both of those groups. In addition, Fe is more highly depleted compared to Ni. The Sm–Nd age of ~2 b.y. is evidence that a partial resetting event took place on the parent body at that time, possibly occurring during an aqueous alteration phase. The chemical composition of Tieschitz can support two petrogenetic scenarios—one in which formation occurred on a parent body unique from that of the H- and L-group ordinary chondrites, and another in which Fe was lost from an H-type chondritic body without disrupting the balance of other elemental systematics.

Tieschitz is texturally unique in that it contains both an opaque (black) matrix component and a transparent (white) matrix component. The white matrix material fills the interstitial space between chondrules and clasts, and is comprised of an amorphous phase primarily composed of albitic plagioclase (Al-, Na-, and Ca-rich) containing nanometer scale inclusions of Ca-rich pyroxene (Dobrică and Brearley, 2011, 2014, 2016). The white matrix is theorized to have precipitated from a leachate of chondrule feldspathic mesostasis glass that was dissolved by an aqueous, halogenated, metasomatic fluid (Dobrică and Brearley, 2014 and references therein). This scenario is consistent with the numerous voids found in ~30% of the chondrules and the observation that the white matrix shares a similar mineralogy with the altered ‘bleached’ chondrules.

The low-alkali black matrix component of Tieschitz also shows the effects of metasomatism (Dobrică and Brearley, 2011). The black matrix contains micron-scale voids and veins, sometimes incorporating a polycrystalline fibrous mineral lining the walls which was determined to be sodic-calcic amphibole, a secondary mineral never before reported in an ordinary chondrite (Dobrică and Brearley, 2014). In addition, elongated ferroan olivine crystals are present within the voids, which were demonstrated to have formed under conditions of low pressure and low water:rock ratios. Both the amphibole and the olivine were precipitated from an aqueous fluid, probably during the same hydrothermal event that produced the voids in the chondrule mesostasis.

Although a Sm–Nd study (Smoliar et al., 2004) suggests that a late alteration event occurred ~2.0 b.y. ago, necessarily involving an impact heating event, the Ar–Ar chronometer has not been disturbed (4.45 [±0.05] b.y.; Turner et al., 1978). Upon consideration of all the evidence, Dobrică and Brearley (2014) argue that the metasomatic process that produced the amphibole-filled voids in the black matrix, and which led to the precipitation of the albitic white matrix, most likely occurred during primary metamorphism on the parent body of Tieschitz through radiogenic heating.

A native Cu assemblage has been identified by Komorowski et al. (2009, 2010, 2012) consisting of nm-sized metallic Hg spherules and HgS (cinnabar), associated with CuS (covellite) and native Cu. This first occurrence of native Hg in a meteorite likely reflects equilibration with subsequent sulfidation processes during accretion of fine-grained dust at low temperatures (<< 300°C) within the nebula. It has been demonstrated that these volatile-rich assemblages are not associated with shock-generated remobilization–condensation scenarios on the parent asteroid.

A wide variety of chondrule types are present in Tieschitz including BO, RP, and POP. Unlike other H3 chondrules, the porphyritic chondrules in Tieschitz have accretionary, fine-grained, dark rims, possibly formed by fine dust from impacts prior to planetary accumulation and lithification. Metal–troilite assemblages also occur in chondrule rims. Flat trace element abundance patterns of refractory lithophiles in nonporphyritic chondrules suggest that they originated by direct nebular condensation, which was followed by metasomatic processes (Engler et al., 2003). A cooling rate of 18°C/m.y. was calculated for Tieschitz based upon cloudy taenite particle size (Scott et al., 2013). This cooling rate, along with other literature cooling rate data for a broad spectrum of meteorite groups having a wide range of metamorphic grades, led to the conclusion that an onion shell model was not appropriate for the ordinary chondrites; instead, thorough impact-generated mixing of all the metamorphic layers after cooling is considered a more scenario.

Anomalous grains including presolar Al-rich oxide grains have been identified in Tieschitz. Most of these anomalous grains are known to originate in red giant stars located ~100 AU from the solar nebula; one particular 17O-rich grain has a composition consistent with an origin from a supernova. Another 17O-depleted grain has a composition more representative of a low mass star like the Sun. Also present are circumstellar grains of graphite, corundum, and spinel, and an abundance of SiC grains; these grains have anomalous isotopic ratios and are considered to have condensed around AGB or J-type stars. The few SiC X-grains present in Tieschitz were probably formed in type II supernovae. From their study of O-isotopic anomalies of the Sun, Lee et al. (2008) inferred that the Sun must have formed within a stellar cluster coeval with a massive star.

It was demonstrated by Szurgot (2016) that the mean atomic weight (Amean) of meteorites can be used to resolve the OC groups, including the intermediate groups L/LL and H/L. Amean values can also be predicted through various equations based on other parameters such as atomic Fe/Si ratio and grain density, and these Amean values, as well as the magnetic susceptibility values derived from X-ray fluorescence (XRF) scanning, all consistently resolve these groups into the ordered sequence LL < L/LL < L < H/L < H. Tieschitz has Amean values of 24.32 (chemical composition), 24.14 (Fe/Si atomic ratio), and 24.30 (grain density). The magnetic susceptibility value for Tieschitz (logχ = 4.91) corresponds to an Amean value of 23.92 utilizing the equation [Amean = 1.49 × logχ + 16.6]. The magnetic susceptibility values determined for both the historical and transitional OC groups are consistent with the ordered sequence above. Furthermore, it was demonstrated that Amean values are lower for unequilibrated type 3 samples than for equilibrated samples within each OC group due to the presence of water; Amean values for petrologic types 4–6 are indistinguishable within each group. standby for amean diagram
Diagram credit: M. Szurgot, 47th LPSC, #2180 (2016)
Amean based on chemical composition (Eq. 1), Fe/Si atomic ratio (Eq. 2), and grain density (Eq. 3) A hypothesis was presented by Trigo-Rodríguez and Williams (2016) to explain the notable coincidence in the timing of the four known H/L chondrite falls—all occurring within a three month period: Bremervorde on May 13, 1855; Famenin on June 27, 2015; Cali on July 6, 2007; and Tieschitz on July 15, 1878. The probability that all of the H/L meteorite falls would occur within this specific timeframe completely by chance was calculated to be only 6%. Trigo-Rodríguez and Williams (2016) consider that these H/L chondrites could be associated with the Bejar bolide that was tracked by the Spanish Meteor Network above Salamanca, Spain on July 11, 2008, and also fortuously photographed from Madrid by Javier Pérez Vallejo. Based on the available data, an orbital solution was constructed for this bolide which is consistent with a high-inclination orbit, and it is considered that it could represent material from the disruption of comet C/1919 Q2 Metcalf (see diagram below). They also propose that the Bejar bolide along with the H/L chondrites could be associated with the Omicron Draconids meteor stream which was shown by A. Cook to follow a similar orbit as comet C/1919 Q2 Metcalf. As demonstrated by Martínez-Jiménez et al. (2016) in their study of the Cali meteorite, not all H/L chondrites show such obvious features of aqueous alteration as those present in Tieschitz. Therefore, the H/L parent asteroid could be heterogeneous with respect to aqueous alteration, or alternatively, it could be a rubble pile composed of a broad diversity of material with variable densities and metamorphic histories. standby for bejar orbit diagram
Diagram credit: Josep M. Trigo-Rodríguez/SPMN Other meteorites assigned to this intermediate chondrite group include Famenin [3.8–3.9], Bremervörde [3.9], NWA 1955 [3–4], Haxtun [4], Yamato 74645 [4], Cali [4], and Yamato 8424; initial studies of Dhofar 008 indicate that it might also belong to this group. The specimen of Tieschitz shown above is a 4.8 g interior cut fragment, and the bottom image is an excellent petrographic thin section micrograph of Tieschitz, shown courtesy of Peter Marmet. standby for tieschitz ts photo
click on image for a magnified view
Photo courtesy of Peter Marmet


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Seemore Downs 001

L/LL4
standby for seemore downs 001 photo
Found April 1991
30° 35′ S., 125° 13′ E. When found in Western Australia, this meteorite was composed of several large fragments and four smaller pieces having a combined weight of 429 g. Seemore Downs might be a chemically extreme member of the L or LL ordinary chondrite groups, or it could be derived from its own unique parent body with properties intermediate to, or overlapping with, both the L and the LL parent bodies.

Previous parameters used to delimit an L/LL group from the L and LL groups include the siderophile element concentrations, the fayalite content in olivine, and the cobalt concentration in kamacite. New studies utilizing cluster anaysis statistics on the minor and trace element data conclude that the L/LL meteorites are chemically more closely related to each other than they are to either the L or LL group. Furthermore, the enriched REE concentration and the negative europium anomaly, which are found only in the L/LL meteorites, easily distinguishes them from the other groups (Friedrich and Lipschutz, 2001). Moreover, it was ascertained by Heck et al. (2009) that the O-isotopic compositions and the major and minor elemental compositions overlap between the L and LL chondrite groups. Since these meteorites do not fit into either of these two groups, they provide evidence for the existence of a separate L/LL, low total-Fe, chondritic parent body. The gas-retention age distribution determined for a set of 12 L/LL chondrites by Wasson and Wang (1991) revealed a different age range for each L, LL, and L/LL group. This suggests that meteorites from these chondrite groups originated from at least three separate parent bodies. At the close of 2009, the Meteoritical Bulletin Database has listed 102 meteorites classified as members of the L/LL group, although a portion of these could reflect an inability of the classifier to adequately distinguish between the L and LL groups.

It was demonstrated by Szurgot (2016) that the mean atomic weight (Amean) of meteorites can be used to resolve the OC groups, including the intermediate groups L/LL and H/L. Amean values can also be predicted through various equations based on other parameters such as atomic Fe/Si ratio, grain density, and magnetic susceptibility, and these Amean values all consistently resolve these groups into the ordered sequence LL < L/LL < L < H/L < H. Furthermore, it was demonstrated that Amean values are lower for unequilibrated type 3 samples than for equilibrated samples within each OC group due to the presence of water; Amean values for petrologic types 4–6 are indistinguishable within each group. standby for amean diagram
Diagram credit: M. Szurgot, 47th LPSC, #2180 (2016)
Amean based on chemical composition (Eq. 1), Fe/Si atomic ratio (Eq. 2), and grain density (Eq. 3) Other members of this intermediate chondrite group include L/LL3 Inman, L/LL4 Bjurböle, L/LL5 Knyahinya, and L/LL6 Naryilco. The specimen of Seemore Downs 001 shown above is an 8.9 g partially crusted fragment.


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Qidong

L/LL5
standby for qidong photo
Fell July 2, 1982
32° 05′ N., 121° 30′ E. A single stone of 1,275 g fell at 5:45 P.M. in Qidong County, Jiangsu province, China. After detonations were heard, the meteorite was found lying in a field. Qidong has a recrystallized texture but chondrules are still obvious, consistent with a petrologic grade of 5. Shock features include extensive fracturing and undulose extinction in silicates, with mosaisicm recognized in some olivines. Fine-grained troilite/metal assemblages are abundant throughout. The vast majority of metal grains are taenite.

Qidong follows metal–silicate trends that are different from those of the recognized ordinary chondrite groups. Evidence for a new intermediate L/LL-chondrite group is becoming well documented. The average olivine fayalite content of 25.7 mole% places Qidong at the extreme higher end of the L group (22.7–25.6 mole%), biased towards the LL group. Still, the Fa in one olivine studied was 28.4 mole%, within the range of the LL group. The average ferrosilite content of 21.5 mole% is at the extreme higher end of the L group (18.7–21.8 mole%), also biased towards the LL group. Qidong has an FeNi-metal abundance of 4.7 wt% placing it at the extreme lower end of the L group (4.4–11.7 wt%) and in the middle of the LL group (3.0–6.0 wt%). Another classification parameter useful for distinguishing between the L and LL groups is the Co abundance (mg/g) in matrix kamacite. An average of 15 mg/g was measured for Qidong, placing it at the extreme lower end of the LL range (15–110) and well outside that of the L range (6.7–8.2).

It was demonstrated by Szurgot (2016) that the mean atomic weight (Amean) of meteorites can be used to resolve the OC groups, including the intermediate groups L/LL and H/L. Amean values can also be predicted through various equations based on other parameters such as atomic Fe/Si ratio, grain density, and magnetic susceptibility, and these Amean values all consistently resolve these groups into the ordered sequence LL < L/LL < L < H/L < H. Furthermore, it was demonstrated that Amean values are lower for unequilibrated type 3 samples than for equilibrated samples within each OC group due to the presence of water; Amean values for petrologic types 4–6 are indistinguishable within each group. standby for amean diagram
Diagram credit: M. Szurgot, 47th LPSC, #2180 (2016)
Amean based on chemical composition (Eq. 1), Fe/Si atomic ratio (Eq. 2), and grain density (Eq. 3) The discovery of several anomalous olivine and pyroxene grains having abnormal Mg# suggests that Qidong is a fragmental breccia. The various components of the breccia must have been mixed by a late impact event after the main period of metamorphism had ended. Final lithification was accomplished through subsequent smaller impact shock events.

Although Qidong is published as a classification of L5, a growing body of evidence is leading to the conclusion that it is another member of an intermediate chondrite group. This group includes L/LL3 Esperance, L/LL4 Seemore Downs, Bjurböle, and Cynthiana, L/LL5/6 Sahara 97021, L/LL6 Acfer 041, and several others. A few meteorites are only partially resolved into the L/LL group, including L/LL3 Inman, L/LL5 Knyahinya, and L/LL6 Holbrook and Sultanpur. The main mass of Qidong is held at the Purple Mountain Observatory, Academia Sinica, in Nanjing, China. The Qidong specimen shown above weighs 2.16 g, and it was cut from a 35 g fragment purchased at the 2001 Macovich Meteorite Auction in Tucson.


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NWA 4156

H/L6
standby for northwest africa 4156 photo
Purchased before 2006
no coordinates recorded Five paired stones having a combined weight of 711.6 g were found in Northwest Africa and sold in Erfoud, Morocco to meteorite collector C. Anger of Austromet. Samples of each stone were submitted for analysis and classification to the Museum für Naturkunde (A. Greshake and M. Kurz), and a NWA-series designation of 4152 through 4156 was assigned to the members of the pairing group. Northwest Africa 4152–4156 was determined to have anomalous silicate ranges; the average Fa value of 20.4 is consistent with the H chondrite group, while the average Fs value of 20.4 is consistent with the L chondrite group. Therefore, it was determined that this pairing group belongs to the transitional H/L chondrite group.

The H/L chondrite group comprises a couple of dozen members, of which some or all might represent a distinct ordinary chondrite parent body. Northwest Africa 4152–4156 is either a representative of this distinct parent body, or alternatively, the anomalous silicate values may indicate that the Fa and Fs ranges for the H and/or L chondrite groups need to be extended. The potential identification of further chemical and petrographic characteristics inconsistent with the known H and L chondrites would help provide a definitive assignment.

ORDINARY CHONDRITE COMPOSITIONS
Fa Fs
H 16–20.4 14.5–18.1
H/L 19.5–21.8 17.2–21.2
L 22–26 18.7–22
L/LL 25.5–26.5
LL 26–33 22–26

H/L chondrite ranges derived from published values for equilibrated H/L members. The petrographic features of this meteorite were determined to be consistent with type 6, which is a very rare type for this transitional group shared by only seven other members. The five meteorites composing the 4152–4156 pairing group have shock stages in the range of S3–S4 and weathering grades in the range of W2–W4. The photo shown above is a 3.31 g partial slice acquired from Christian Anger which was cut from the 165 g NWA 4156 stone. Thank you dearly departed friend.