Abstract:Meteorites are fascinating cosmic visitors. Using accessible language, this book documents the history of mineralogy and meteorite research, summarizes the mineralogical characteristics of the myriad varieties of meteorites, and explains the mineralogical characteristics of Solar System bodies visited by spacecraft. Some of these bodies contain minerals that do not occur naturally on Earth or in meteorites. The book explains how to recognize different phases under the microscope and in back-scattered electron… Show more
“…(2014) provide a definition of a chemical group, similar to that given by Weisberg et al. (2006) and Rubin and Ma (2021) and which may be held to be consensual:Conventionally, a chondrite “group” is defined as having a minimum of five unpaired chondrites of similar mineralogy, petrography, bulk isotopic properties, and bulk chemical compositions in major, nonvolatile elements.…”
Section: What Is a Group?mentioning
confidence: 99%
“…Howardites, eucrites, and diogenites are ranked as three different “groups” yet share the same parent body, so the parent body taxon is rather the HED clan. Rubin and Ma (2021) systematically use the word “clan” to mean putative parent body taxa for differentiated meteorites. So “groups” refer there to specific lithologies inside a parent body.…”
Section: What Is a Group?mentioning
confidence: 99%
“…Here, the ordinary chondrite (OC) clan is distinguished from the more inclusive O group, which comprises differentiated meteorites (e.g., IIE irons); same for EC versus E and CC versus C (see the Chondrites section). I show in dotted magenta the nameless Rubin and Ma (2021) HED‐MES‐PMG‐IIIAB “superclass,” which is a group in our parlance. All mentioned high‐level groups are meaningful whether they represent one or several primary parent bodies, hence the impossibility to define a real hierarchy among them except locally for nested groups.…”
Section: A Proposed Classificationmentioning
confidence: 99%
“…For chondrites, Krot et al (2014) provide a definition of a chemical group, similar to that given by Weisberg et al (2006) and Rubin and Ma (2021) and which may be held to be consensual: Fig. 1.…”
Section: What Is a Group?mentioning
confidence: 99%
“…Their other "superclass," that of the enstatite meteorites, corresponds to the E group in this paper. It may be noted that "classes" in the sense of Rubin and Ma [2021] also carry a genetic connotation, as grouping "one or more clans that formed in the same general region of the solar system." It is seen that there is little qualitative difference between the definitions of these two levels of the hierarchical system of Rubin and Ma [2021], and one of my chief points here is that it cannot be otherwise.…”
The current meteorite taxonomy, a result of two centuries of meteorite research and tradition, entangles textural and genetic terms in a less than consistent fashion, with some taxa (like "shergottites") representing varied lithologies from a single putative parent body while others (like "pallasites") subsume texturally similar objects of multifarious solar system origins. The familiar concept of "group" as representative of one primary parent body is also difficult to define empirically. It is proposed that the classification becomes explicitly binominal throughout the meteorite spectrum, with classes referring to petrographically defined primary rock types, whereas groups retain a genetic meaning, but no longer tied to any assumption on the number of represented parent bodies. The classification of a meteorite would thus involve both a class and a group, in a twodimensional fashion analogous to the way Van Schmus and Wood decoupled primary and secondary properties in chondrites. Since groups would not substantially differ, at first, from those in current use de facto, the taxonomic treatment of "normal" meteorites, whose class would bring no new information, would hardly change. Yet classes combined with high-or low-level groups would provide a standardized grid to characterize petrographically and/or isotopically unusual or anomalous meteorites-which make up the majority of represented meteorite parent bodies-for example, in relation to the carbonaceous/ noncarbonaceous dichotomy. In the longer term, the mergers of genetically related groups, a more systematic treatment of lithology mixtures, and the chondrite/achondrite transition can further simplify the nomenclature.
“…(2014) provide a definition of a chemical group, similar to that given by Weisberg et al. (2006) and Rubin and Ma (2021) and which may be held to be consensual:Conventionally, a chondrite “group” is defined as having a minimum of five unpaired chondrites of similar mineralogy, petrography, bulk isotopic properties, and bulk chemical compositions in major, nonvolatile elements.…”
Section: What Is a Group?mentioning
confidence: 99%
“…Howardites, eucrites, and diogenites are ranked as three different “groups” yet share the same parent body, so the parent body taxon is rather the HED clan. Rubin and Ma (2021) systematically use the word “clan” to mean putative parent body taxa for differentiated meteorites. So “groups” refer there to specific lithologies inside a parent body.…”
Section: What Is a Group?mentioning
confidence: 99%
“…Here, the ordinary chondrite (OC) clan is distinguished from the more inclusive O group, which comprises differentiated meteorites (e.g., IIE irons); same for EC versus E and CC versus C (see the Chondrites section). I show in dotted magenta the nameless Rubin and Ma (2021) HED‐MES‐PMG‐IIIAB “superclass,” which is a group in our parlance. All mentioned high‐level groups are meaningful whether they represent one or several primary parent bodies, hence the impossibility to define a real hierarchy among them except locally for nested groups.…”
Section: A Proposed Classificationmentioning
confidence: 99%
“…For chondrites, Krot et al (2014) provide a definition of a chemical group, similar to that given by Weisberg et al (2006) and Rubin and Ma (2021) and which may be held to be consensual: Fig. 1.…”
Section: What Is a Group?mentioning
confidence: 99%
“…Their other "superclass," that of the enstatite meteorites, corresponds to the E group in this paper. It may be noted that "classes" in the sense of Rubin and Ma [2021] also carry a genetic connotation, as grouping "one or more clans that formed in the same general region of the solar system." It is seen that there is little qualitative difference between the definitions of these two levels of the hierarchical system of Rubin and Ma [2021], and one of my chief points here is that it cannot be otherwise.…”
The current meteorite taxonomy, a result of two centuries of meteorite research and tradition, entangles textural and genetic terms in a less than consistent fashion, with some taxa (like "shergottites") representing varied lithologies from a single putative parent body while others (like "pallasites") subsume texturally similar objects of multifarious solar system origins. The familiar concept of "group" as representative of one primary parent body is also difficult to define empirically. It is proposed that the classification becomes explicitly binominal throughout the meteorite spectrum, with classes referring to petrographically defined primary rock types, whereas groups retain a genetic meaning, but no longer tied to any assumption on the number of represented parent bodies. The classification of a meteorite would thus involve both a class and a group, in a twodimensional fashion analogous to the way Van Schmus and Wood decoupled primary and secondary properties in chondrites. Since groups would not substantially differ, at first, from those in current use de facto, the taxonomic treatment of "normal" meteorites, whose class would bring no new information, would hardly change. Yet classes combined with high-or low-level groups would provide a standardized grid to characterize petrographically and/or isotopically unusual or anomalous meteorites-which make up the majority of represented meteorite parent bodies-for example, in relation to the carbonaceous/ noncarbonaceous dichotomy. In the longer term, the mergers of genetically related groups, a more systematic treatment of lithology mixtures, and the chondrite/achondrite transition can further simplify the nomenclature.
Within this work, we present the first true three‐dimensional (3D) analysis of chondrule size. Knowledge about the physical properties of chondrules is important for validating astrophysical theories concerning chondrule formation and their aggregation into the chondritic meteorites (known as chondrites) that contain them. The classification of chondrites into chemical groups also relies on chondrule properties, including their dimensions. Within this work, we quantify the diameters of chondrules in five ordinary chondrites (OCs; comprised of the H, L, and LL chondrites) and one low‐iron enstatite (EL) chondrite. To extract the chondrule size data, we use x‐ray computed microtomography to image small (~1–2 cm3) chondrite samples followed by manual digital segmentation to isolate chondrules within the volumes or subvolumes. Our data yield true 3D results without stereographic corrections necessary for two‐dimensional (2D) or petrographic thin section‐based determinations of chondrule sizes. Our results are completely novel, but are consistent with previous surface analysis (2D) data for OCs. Within our OC chondrule diameter data, we find the trend of mean chondrule diameters increasing in the order H < L < LL. We also present the first detailed EL chondrite chondrule size‐frequency distribution. Finally, we examine the shapes and collective orientations of the chondrules within the chondrites and show that chondrite petrofabrics can be explored with our methodology. Chondrule shape‐preferred orientations are identical to the orientations of the metal and sulfide grains in the chondrites and this is likely due to impact‐related compaction.
Highlights
We present a first true three‐dimensional analysis of chondrule size.
Our ordinary chondrite chondrule diameter data demonstrate the trend of mean chondrule diameters increasing in the order H chondrites < L chondrites < LL chondrites.
We also present the first detailed low‐iron enstatite chondrite chondrule size‐frequency distribution.
We examine the shapes and collective orientations of the chondrules and show that chondrite petrofabrics can be explored with our methodology.
Diogenites are thought to have originated from asteroid 4 Vesta asteroid, and it has been previously shown that they mostly consist of orthopyroxene, chromite, and olivine minerals. In this study, the Aioun El Atrouss (AAT‐1) diogenite was analyzed by vibrational spectroscopic (FT‐IR and micro‐Raman), EDXRF, and XRD techniques. AAT‐001 is mainly composed of pyroxene and with lesser olivine. XRD investigation confirmed magnetite, kamacite, ilmenite, and albite. A troilite‐orthopyroxene intergrowth was revealed by XRF. The olivine composition was estimated to be approximately Fo66 by Raman olivine characteristic doublets. Pyroxenes in AAT‐01 were found to be En80Fs20. Finally, approximate peak shock pressure of more than 86 GPa for AAT‐1 was suggested based on previous hypervelocity impact experiments on olivine.
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