An achondrite is a type of stony meteorite whose precursor was of chondritic origin and experienced metamorphic and igneous processes. They have a planetary or differentiated asteroidal origin where the chondritic parent body reached a sufficient size that through heating due to radioactive decay of 26Al (isotope of Aluminum) and Click on Term to Read More, Modifying term used to describe meteorites that are mineralogically and/or chemically unique and defy classification into the group or sub-group they most closely resemble. Some examples include Ungrouped Achondrite (achondrite-ung), Ungrouped Chondrite (chondrite-ung), Ungrouped Iron (iron-ung), and Ungrouped Carbonaceous (C-ung). Click on Term to Read More
(Ureilite [olivine-augite type] in MetBull 87)
no coordinates recorded
click on image for a magnified view Diagram credit: Beard et al., 81st MetSoc, #6170 (2018) Results of an in-depth study of this anomalous meteorite were presented by C. Goodrich et al. (2005, 2006). They found that many of the petrologic features of NWA 1500 were in fact consistent with accumulation on the ureilite parent body from a high degree fractional melt, which occurred at a greater depth than that at which the most ferroan olivine–Low-Ca clinopyroxene, (Ca,Mg,Fe)SiO3, found as a major mineral in eucrites and shergottites. In order to be considered pigeonite, the clinopyroxene must contain 5 to 20 mol % of calcium (Wo5 - 20). Chondrites of petrologic types 4 and below contain significant low-Ca clinopyroxene. During metamorphism to higher temperatures, all existing ureilites formed. The Fe–Mn–Mg composition of olivine in NWA 1500 is consistent with the ratios measured for other augite-bearing ureilites, but it would be a ureilite that contains a larger melt component and has undergone a higher degree of smelting/reduction. In a subsequent study, Goodrich et al. (2006) provided many examples of textural, chemical, and mineralogical characteristics of NWA 1500 which are consistent with the augite-bearing ureilite group, and they proposed that this is a member of the small group of augite-bearing (lacking pigeonite), monomict ureilites. To account for the many anomalous characteristics shown by NWA 1500, they argued that it experienced higher Oxidation 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 Click on Term to Read More given its greater depth of formation, and that it subsequently experienced only slight reduction during ascent as shown by the reverse zoning of olivine; examination of other brachinites for reverse zoning in olivine grains will be beneficial. Low Cr and P in olivine and metal, and the presence of chromite and apatite phases, are also indicative of higher oxidation conditions for this ureilite during formation at greater depth. The presence of plagioclase as poikilitic and intergranular grains is indicative of Physical or chemical process or action that results in the formation of regularly-shaped, -sized, and -patterned solid forms known as crystals. Click on Term to Read More from a melt at great depth, and this feature further distinguishes this possible ureilite from all others. Northwest Africa 1500 was equilibrated at lower temperatures than any other ureilite measured, which is consistent with the generally accepted ureilite model involving a breakup with subsequent rapid cooling of its parent body during its magmatic stage. Further studies of NWA 1500 by Goodrich et al. (2011) determined that texture, modal abundances, Inorganic 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 Click on Term to Read More compositions, Often abbreviated as “REE”, these 16 elements include (preceded by their atomic numbers): 21 scandium (Sc), 39 Yttrium (Y) and the 14 elements that comprise the lanthanides excluding 61 Promethium, an extremely rare and radioactive element. These elements show closely related geochemical behaviors associated with their filled 4f atomic orbital. Click on Term to Read More abundances, O-isotopic compositions, and Literally, "iron-loving" element that tends to be concentrated in Fe-Ni metal rather than in silicate; these are Fe, Co, Ni, Mo, Re, Au, and PGE. These elements are relatively common in undifferentiated meteorites, and, in differentiated asteroids and planets, are found in the metal-rich cores and, consequently, extremely rare on abundances all follow brachinite trends, and are distinguishable from other olivine-rich, primitive achondrite groups. However, through studies of highly siderophile Substance 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 Click on Term to Read More (HSE) abundances, and upon examining the metal-sulfide segregation processes, it was determined by Day et al. (2012) that NWA 1500 and similar brachinite-like primitive achondrites were not likely genetically related (i.e. from the same parent body) to brachinites, but rather, originated on similar volatile-rich, Oxidation 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 Click on Term to Read More, chondritic precursor asteroids while experiencing similar petrologic processes during their history. Goodrich et al. (2017) determined that brachinites and brachinite-like achondrites have a distinct Oxidation 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 Click on Term to Read More trend and a higher Fe/Mg ratio compared to all other primitive achondrites, consistent with formation in a similar An 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 Click on Term to Read More reservoir; therefore, they suggest that brachinites and brachinite-like achondrites be called the brachinite clan. Notably, an achondrite A mineral or rock fragment embedded in another rock. Click on Term to Read More from the Kaidun meteorite has been favorably compared to a brachinite (Higashi et al., 2017, #1874). Verification of this discovery would infer a very old formation age for the Kaidun parent body, since the age of Brachina is 4.564.8 (±0.0005) b.y. The specimen of NWA 1500 shown above is a 3.97 g partial slice.