scholarly journals Presolar grains in primitive ungrouped carbonaceous chondrite Northwest Africa 5958

2019 ◽  
Vol 55 (6) ◽  
pp. 1160-1175 ◽  
Author(s):  
Larry R. Nittler ◽  
Rhonda M. Stroud ◽  
Conel M. O'D. Alexander ◽  
Kaitlin Howell
Keyword(s):  
Carbonaceous Chondrite ◽  
Presolar Grains ◽  
Northwest Africa

scholarly journals New carbonaceous chondrite Northwest Africa 11781 (CM2)

LITOSFERA ◽  
2019 ◽  
Vol 19 (4) ◽  
pp. 580-587
Author(s):  
Kseniya A. Dugushkina ◽  
◽  
Stepan V. Berzin ◽  
Keyword(s):  
Carbonaceous Chondrite ◽  
Northwest Africa

Momentum transfer in hypervelocity cratering of meteorites and meteorite analogs: Implications for asteroid deflection

2019 ◽  
Author(s):  
George J. Flynn ◽  
Daniel D. Durda ◽  
Mason J. Molesky ◽  
Brian A. May ◽  
Spenser N. Congram ◽  
...  
Keyword(s):  
Significant Contribution ◽  
Carbonaceous Chondrite ◽  
Ordinary Chondrite ◽  
Reflection Spectra ◽  
Porous Rock ◽  
Northwest Africa ◽  
Wide Range ◽  
Asteroid Deflection ◽  
Post Impact ◽  
Highly Porous

Abstract Asteroid porosity ranges from 0 to >50%, with most >20%, and some asteroids exhibit a water feature in their reflection spectra. Porosity and hydration are expected to influence the momentum transferred in hypervelocity collisions. We conducted a series of measurements of the post-impact momentum, characterized by a factor β, the ratio of the total linear momentum acquired by the target to the momentum of the impactor. We measured β for anhydrous meteorites, samples of their asteroidal parent bodies, spanning a wide range of porosities: 7 samples of the CV3 carbonaceous chondrite Northwest Africa (NWA) 4502 (2.1% porosity), 7 samples of the ordinary chondrite NWA 869 (6.4% porosity), and 4 samples of the ordinary chondrite Saratov (15.6% porosity), as well as 2 samples of terrestrial pumice (80% porosity). We also measured hydrous meteorite analog targets, including 2 samples of terrestrial serpentine (17.9% porosity) and 4 samples of terrestrial montmorillonite (51.5% porosity), the two clay minerals that dominate the composition of the hydrous CI carbonaceous chondrite meteorites, as well as 4 samples of hydrous meteorite analog material prepared by powdering and hydrating an anhydrous carbonaceous chondrite. We found that for both anhydrous and hydrous samples β decreased with increasing porosity, consistent with hydrocode modeling. The β for each target type was >2 demonstrating that crater ejecta makes a significant contribution to recoil in hypervelocity collisions.. The β values we measured for the anhydrous samples are larger, with β = 3.55 for NWA 4502, 2.69 for NWA 869, 2.10 for Saratov, and 2.15 for pumice, than results from hydrocode modeling for 10 km/s impacts into relatively strong, porous rock targets. The momentum enhancement by ejecta (β - 1) for the moderate porosity (17.9%) hydrous serpentine targets (β = 4.70), the highly porous (51.55% porosity) hydrous montmorillonite targets (β = 2.79), and the intermediate porosity (~26%) CI-analogs (β = 2.99) are much larger than β value for anhydrous targets of similar porosity, indicating jetting of water vapor could significantly affect deflection of hydrous asteroids and comets in natural or human-induced collisions.

HRTEM study of valleriite, a hydroxide-bearing copper sulfide

1990 ◽  
Vol 48 (4) ◽  
pp. 462-463
Author(s):  
S. Wang ◽  
P. R. Buseck
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Copper Sulfide ◽  
Carbonaceous Chondrite ◽  
Structural Data ◽  
Basic Structure ◽  
Long Period ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Wavy Structure

Valleriite is an unusual mineral, consisting of intergrowths of sulfide layers (corresponding in structure to the mineral smythite - Fe9S11) and hydroxide layers (corresponding to brucite - Mg(OH2)). It has a composition of approximately 1.526[Mg.68Al.32(OH)2].[Fe1.07Cu.93S2] and consists of two interpenetrating lattices, each of which retains its individual structural and diffraction characteristics parallel to the layering. The valleriite structure is related to that of tochilinite, an unusual iron-rich mineral that is of considerable interest for the origin of certain carbonaceous chondrite meteorites and to those of franckeite and cylindrite, two minerals that are of interest because of their unique morphological and crystallographic properties, e.g., the distinctive curved form of cylindrite and the perfect mica-like cleavage with unusual striations and the long-period wavy structure of franckeite.Our selected-area electron diffraction (SAED) patterns and high-resolution transmission electron microscope (HRTEM) images of valleriite provide new structural data. A basic structure and a new superstructure have been observed.

LITHOLOGIC DIVERSITY WITHIN LUNAR REGOLITH BRECCIA METEORITE NORTHWEST AFRICA 8783: CLASTS 3 AND 6

2020 ◽  
Author(s):  
Cecillia Utterback ◽  
◽  
Madi Hall ◽  
Erin M. Recchuiti ◽  
Amy L. Fagan
Keyword(s):  
Lunar Regolith ◽  
Northwest Africa

scholarly journals Molecular Species Delimitation of Larks (Aves: Alaudidae), and Integrative Taxonomy of the Genus Calandrella, with the Description of a Range-Restricted African Relic Taxon

Diversity ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 428
Author(s):  
Martin Stervander ◽  
Bengt Hansson ◽  
Urban Olsson ◽  
Mark F. Hulme ◽  
Ulf Ottosson ◽  
...  
Keyword(s):  
Mitochondrial Dna ◽  
Molecular Species ◽  
Species Delimitation ◽  
Integrative Taxonomy ◽  
West African ◽  
Northwest Africa ◽  
Sub Saharan ◽  
Plateau State ◽  
Avian Family ◽  
Relic Population

Larks constitute an avian family of exceptional cryptic diversity and striking examples of convergent evolution. Therefore, traditional morphology-based taxonomy has recurrently failed to reflect evolutionary relationships. While taxonomy ideally should integrate morphology, vocalizations, behaviour, ecology, and genetics, this can be challenging for groups that span several continents including areas that are difficult to access. Here, we combine morphometrics and mitochondrial DNA to evaluate the taxonomy of Calandrella larks, with particular focus on the African C. cinerea and the Asian C. acutirostris complexes. We describe a new range-restricted West African taxon, Calandrella cinerea rufipecta ssp. nov. (type locality: Jos, Plateau State, Nigeria), with an isolated relic population 3000 km from its closest relative in the Rift Valley. We performed molecular species delimitation, employing coalescence-based multi-rate Poisson Tree Processes (mPTP) on cytochrome b sequences across 52 currently recognized lark species, including multiple taxa currently treated as subspecies. Three species-level splits were inferred within the genus Calandrella and another 13 across other genera, primarily among fragmented sub-Saharan taxa and taxa distributed from Northwest Africa to Arabia or East Africa. Previously unknown divergences date back as far as to the Miocene, indicating the presence of currently unrecognized species. However, we stress that taxonomic decisions should not be based on single datasets, such as mitochondrial DNA, although analyses of mitochondrial DNA can be a good indicator of taxa in need of further integrative taxonomic assessment.

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