{"id":{"repo_id":"unm","oai_identifier":"oai:digitalrepository.unm.edu:eps_etds-1006"},"canonical_url":"https://search.dev.ndltd.org/etd/unm/oai:digitalrepository.unm.edu:eps_etds-1006","repository":{"repo_id":"unm","name":"University of New Mexico","base_url":"https://digitalrepository.unm.edu/do/oai/"},"display":{"title":"A TEM study of crystalline silicates in the matrices of MET 00426 and QUE 99177 CR3.0 chondrites: Constraints on the formation mechanisms of dust in the solar nebula","abstract":"Understanding the constituents of fine-grained nebular dust prior to asteroidal accretion is a significant challenge in meteoritics. The key to understanding nebular dust lies in chondritic meteorites, which are composed of undifferentiated solar system materials. Chondritic matrices are a subnanometer mixture of amorphous material, silicate grains, sulfides, and other phases, that act as the \"glue\" for larger components. In the pristine chondrites (petrologic type 3.00) the matrix preserves some record of the primary characteristics of nebular dust. Two CR carbonaceous chondrites, MET 00426 (CR3.00) and QUE 99177 (CR3.00), are likely the most pristine meteorites ever described (Abreu and Brearley, 2010). The mineralogy of crystalline silicate grains in the matrices of these two chondrites has been studied here using focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. Dark-field scanning transmission electron microscopy (STEM) imaging, along with bright-field TEM and energy dispersive X-Ray spectroscopy (EDS) techniques were used to understand mineralogical and chemical characteristics. FIB sections consist of extremely fine-grained, amorphous material (<50 nm in size). Additionally, each section contains crystalline or nanocrystalline silicate grains, varying in size from <100 to 1000 nm in diameter. These grains are MgO-rich or FeO-bearing olivines and pyroxenes. These crystalline silicates exhibit unequilibrated major and minor element compositions, but distinct compositional groupings of olivines and pyroxenes can be identified. We infer that the crystalline silicate materials in the matrices of these chondrites formed by different mechanisms that include nebular condensation under equilibrium and disequilibrium conditions, followed in some cases by annealing prior to accretion. Our data discount chondrule fragmentation as a significant source of the fine-grained matrix olivines. Although these chondrites have similar matrix mineralogy and chemistry, FeO-bearing crystalline silicates are more common in MET 00426 matrix than in QUE 99177, indicating that the matrices of these chondrites did not sample the same reservoir or source of crystalline silicate nebular dust. Nevertheless, in many cases, these grains have are similar in composition to other primitive silicates, like interplanetary dust particles (IDPs) and amoeboid olivine aggregates (AOAs), and could share a common formational mechanism or represent the nanoscale equivalent of these objects.","abstract_html":"Understanding the constituents of fine-grained nebular dust prior to asteroidal accretion is a significant challenge in meteoritics. The key to understanding nebular dust lies in chondritic meteorites, which are composed of undifferentiated solar system materials. Chondritic matrices are a subnanometer mixture of amorphous material, silicate grains, sulfides, and other phases, that act as the &quot;glue&quot; for larger components. In the pristine chondrites (petrologic type 3.00) the matrix preserves some record of the primary characteristics of nebular dust. Two CR carbonaceous chondrites, MET 00426 (CR3.00) and QUE 99177 (CR3.00), are likely the most pristine meteorites ever described (Abreu and Brearley, 2010). The mineralogy of crystalline silicate grains in the matrices of these two chondrites has been studied here using focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. Dark-field scanning transmission electron microscopy (STEM) imaging, along with bright-field TEM and energy dispersive X-Ray spectroscopy (EDS) techniques were used to understand mineralogical and chemical characteristics. FIB sections consist of extremely fine-grained, amorphous material (&lt;50 nm in size). Additionally, each section contains crystalline or nanocrystalline silicate grains, varying in size from &lt;100 to 1000 nm in diameter. These grains are MgO-rich or FeO-bearing olivines and pyroxenes. These crystalline silicates exhibit unequilibrated major and minor element compositions, but distinct compositional groupings of olivines and pyroxenes can be identified. We infer that the crystalline silicate materials in the matrices of these chondrites formed by different mechanisms that include nebular condensation under equilibrium and disequilibrium conditions, followed in some cases by annealing prior to accretion. Our data discount chondrule fragmentation as a significant source of the fine-grained matrix olivines. Although these chondrites have similar matrix mineralogy and chemistry, FeO-bearing crystalline silicates are more common in MET 00426 matrix than in QUE 99177, indicating that the matrices of these chondrites did not sample the same reservoir or source of crystalline silicate nebular dust. Nevertheless, in many cases, these grains have are similar in composition to other primitive silicates, like interplanetary dust particles (IDPs) and amoeboid olivine aggregates (AOAs), and could share a common formational mechanism or represent the nanoscale equivalent of these objects.","abstract_has_math":false,"creators":["Brunner, Chelsea"],"institution":null,"degree_name":"Earth and Planetary Sciences","degree_level":"Masters","degree_discipline":"Department of Earth and Planetary Sciences","degree_department":null,"school":null,"contributors":["Brearley, Adrian","Jones, Rhian","Sharp, Zachary","Shearer, Charles"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2012,"date_issued":"2012-05-01T07:00:00Z","date_published":"2012-05-01T07:00:00Z","updated_at":"2026-07-24T05:26:14Z","subjects":["chondrites","matrix","solar nebula","solar system evolution"],"languages":["English"],"rights":[],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://digitalrepository.unm.edu/eps_etds/7"],"render_values":[{"text":"https://digitalrepository.unm.edu/eps_etds/7","href":"https://digitalrepository.unm.edu/eps_etds/7","code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/1928/24645","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Brearley, Adrian","Jones, Rhian","Sharp, Zachary","Shearer, Charles"]},{"key":"dc:creator","label":"Author","values":["Brunner, Chelsea"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"thesis:degree_discipline","label":"Discipline","values":["Department of Earth and Planetary Sciences"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Masters","Thesis"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Earth and Planetary Sciences"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["chondrites","matrix","solar nebula","solar system evolution"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["English"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/1928/24645","https://digitalrepository.unm.edu/eps_etds/7"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Understanding the constituents of fine-grained nebular dust prior to asteroidal accretion is a significant challenge in meteoritics. The key to understanding nebular dust lies in chondritic meteorites, which are composed of undifferentiated solar system materials. Chondritic matrices are a subnanometer mixture of amorphous material, silicate grains, sulfides, and other phases, that act as the \"glue\" for larger components. In the pristine chondrites (petrologic type 3.00) the matrix preserves some record of the primary characteristics of nebular dust. Two CR carbonaceous chondrites, MET 00426 (CR3.00) and QUE 99177 (CR3.00), are likely the most pristine meteorites ever described (Abreu and Brearley, 2010). The mineralogy of crystalline silicate grains in the matrices of these two chondrites has been studied here using focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. Dark-field scanning transmission electron microscopy (STEM) imaging, along with bright-field TEM and energy dispersive X-Ray spectroscopy (EDS) techniques were used to understand mineralogical and chemical characteristics. FIB sections consist of extremely fine-grained, amorphous material (<50 nm in size). Additionally, each section contains crystalline or nanocrystalline silicate grains, varying in size from <100 to 1000 nm in diameter. These grains are MgO-rich or FeO-bearing olivines and pyroxenes. These crystalline silicates exhibit unequilibrated major and minor element compositions, but distinct compositional groupings of olivines and pyroxenes can be identified. We infer that the crystalline silicate materials in the matrices of these chondrites formed by different mechanisms that include nebular condensation under equilibrium and disequilibrium conditions, followed in some cases by annealing prior to accretion. Our data discount chondrule fragmentation as a significant source of the fine-grained matrix olivines. Although these chondrites have similar matrix mineralogy and chemistry, FeO-bearing crystalline silicates are more common in MET 00426 matrix than in QUE 99177, indicating that the matrices of these chondrites did not sample the same reservoir or source of crystalline silicate nebular dust. Nevertheless, in many cases, these grains have are similar in composition to other primitive silicates, like interplanetary dust particles (IDPs) and amoeboid olivine aggregates (AOAs), and could share a common formational mechanism or represent the nanoscale equivalent of these objects."]},{"key":"dc:title","label":"Title","values":["A TEM study of crystalline silicates in the matrices of MET 00426 and QUE 99177 CR3.0 chondrites: Constraints on the formation mechanisms of dust in the solar nebula"]}]}],"canonical_facts":{"dc:contributor":["Brearley, Adrian","Jones, Rhian","Sharp, Zachary","Shearer, Charles"],"dc:creator":["Brunner, Chelsea"],"dc:description.abstract":["Understanding the constituents of fine-grained nebular dust prior to asteroidal accretion is a significant challenge in meteoritics. The key to understanding nebular dust lies in chondritic meteorites, which are composed of undifferentiated solar system materials. Chondritic matrices are a subnanometer mixture of amorphous material, silicate grains, sulfides, and other phases, that act as the \"glue\" for larger components. In the pristine chondrites (petrologic type 3.00) the matrix preserves some record of the primary characteristics of nebular dust. Two CR carbonaceous chondrites, MET 00426 (CR3.00) and QUE 99177 (CR3.00), are likely the most pristine meteorites ever described (Abreu and Brearley, 2010). The mineralogy of crystalline silicate grains in the matrices of these two chondrites has been studied here using focused ion beam (FIB) and transmission electron microscopy (TEM) techniques. Dark-field scanning transmission electron microscopy (STEM) imaging, along with bright-field TEM and energy dispersive X-Ray spectroscopy (EDS) techniques were used to understand mineralogical and chemical characteristics. FIB sections consist of extremely fine-grained, amorphous material (<50 nm in size). Additionally, each section contains crystalline or nanocrystalline silicate grains, varying in size from <100 to 1000 nm in diameter. These grains are MgO-rich or FeO-bearing olivines and pyroxenes. These crystalline silicates exhibit unequilibrated major and minor element compositions, but distinct compositional groupings of olivines and pyroxenes can be identified. We infer that the crystalline silicate materials in the matrices of these chondrites formed by different mechanisms that include nebular condensation under equilibrium and disequilibrium conditions, followed in some cases by annealing prior to accretion. Our data discount chondrule fragmentation as a significant source of the fine-grained matrix olivines. Although these chondrites have similar matrix mineralogy and chemistry, FeO-bearing crystalline silicates are more common in MET 00426 matrix than in QUE 99177, indicating that the matrices of these chondrites did not sample the same reservoir or source of crystalline silicate nebular dust. Nevertheless, in many cases, these grains have are similar in composition to other primitive silicates, like interplanetary dust particles (IDPs) and amoeboid olivine aggregates (AOAs), and could share a common formational mechanism or represent the nanoscale equivalent of these objects."],"dc:identifier":["http://hdl.handle.net/1928/24645","https://digitalrepository.unm.edu/eps_etds/7"],"dc:language":["English"],"dc:subject":["chondrites","matrix","solar nebula","solar system evolution"],"dc:title":["A TEM study of crystalline silicates in the matrices of MET 00426 and QUE 99177 CR3.0 chondrites: Constraints on the formation mechanisms of dust in the solar nebula"],"thesis:degree_discipline":["Department of Earth and Planetary Sciences"],"thesis:degree_level":["Masters","Thesis"],"thesis:degree_name":["Earth and Planetary Sciences"]},"updated_at":"2026-07-24T05:26:14Z"}