ChondrulesRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
Purchased October 2007
no coordinates recorded A single weathered (W3) meteoriteWork in progress. A solid natural object reaching a planet’s surface from interplanetary space. Solid portion of a meteoroid that survives its fall to Earth, or some other body. Meteorites are classified as stony meteorites, iron meteorites, and stony-iron meteorites. These groups are further divided according to their mineralogy and Click on Term to Read More weighing 1,276 g was found in Algeria and sold to a meteorite dealer in Erfoud, Morocco. Analysis and classification of the stone was conducted at Northern Arizona University (T. Bunch and J. Wittke), and it was determined that NWA 5206 is a very weakly shocked (S2), terrestrially weathered (W3), highly unequilibrated LL3.05 (or possibly lower) chondriteChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More.
of both type-I and type-II compositions are present in a ratio of 3:1, respectively. ChondruleRoughly spherical aggregate of coarse crystals formed from the rapid cooling and solidification of a melt at ~1400 ° C. Large numbers of chondrules are found in all chondrites except for the CI group of carbonaceous chondrites. Chondrules are typically 0.5-2 mm in diameter and are usually composed of olivine Click on Term to Read More
textures span a broad range; porphyritic types predominate, while the remainder comprises granular, radial, cryptocrystallineCrypto meaning "hidden" refers to a rock texture in which individual crystals are too small to be distinguished even using a standard petrographic microscope. Crystals are typically less than a few μm in size - any smaller and the texture would be considered amorphous. Among sedimentary terrestrial rocks, chert and Click on Term to Read More
, barred, and a number of unique types, some with thick mantles. In addition to the primitive compositional heterogeneity of this chondrite, other petrographic and chemical characteristics, such as the alkali-poor glassy chondrule mesostasisLast material to crystallize/solidify from a melt. Mesostasis can be found in both chondrules, in the matrix around chondrules, and in achondrites as interstitial fine-grained material such as plagioclase, and/or as glass between crystalline minerals. Click on Term to Read More
and the Cr distribution in ferroan olivineGroup of silicate minerals, (Mg,Fe)2SiO4, with the compositional endpoints of forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine is commonly found in all chondrites within both the matrix and chondrules, achondrites including most primitive achondrites and some evolved achondrites, in pallasites as large yellow-green crystals (brown when terrestrialized), in the silicate portion Click on Term to Read More
, has led investigators to conclude that NWA 5206 is highly unequilibrated with a subtype <3.1. A more extensive review of the most recent techniques used to discriminate among the lowest petrologic types can be found on the NWA 1756
Utilizing Al–Mg chronometry for a broad sampling of unequilibrated ordinary chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such Click on Term to Read More
, Pape et al.
(2019) ascertained that five type-II chondrules from NWA 5206 provide 26
Mg isochron ages of ~1.97 to ~2.64 m.y. after formation of CAIsSub-millimeter to centimeter-sized amorphous objects found typically in carbonaceous chondrites and ranging in color from white to greyish white and even light pink. CAIs have occasionally been found in ordinary chondrites, such as the L3.00 chondrite, NWA 8276 (Sara Russell, 2016). CAIs are also known as refractory inclusions since they Click on Term to Read More
. The total age range for the entire sample set is ~1.76 to ~2.92 m.y. after CAIs, attesting to chondrule formation occurring over an interval of ~1.2 m.y., or ~1.5 m.y. when including the oldest known chondrules.
Diagram credit: Pape et al.
, vol. 244, p. 429 (2019) ‘Time and duration of chondrule formation: Constraints from 26Al-26Mg ages of individual chondrules’
Very few ordinary chondrites have been classified as petrologic subtype 3.05 or lower, and NWA 5206 is the only LL chondriteOrdinary chondrites ("low Fe" / "low metal") with only 1 to 3% free metal. Their olivine is more Fe-rich than in the other ordinary chondrites (Fa27-32), implying that the LL types must have formed under more oxidizing conditions than their H or L cousins. Orthopyroxene compositions are also Fe-the rich Click on Term to Read More
designated as such. A comprehensive pictorial review of NWA 5206 can be found on the Meteorites Australia
page showing examples of the many chondrule types and exotic components such as metallic chondrules armored with troiliteBrass colored non-magnetic Fe sulfide, FeS, found in a variety of meteorites.
, xenolithic chondrule fields, and dark inclusions. The specimen of NWA 5206 shown above is a 7.47 g partial slice. The photo below shows a view of the main massLargest fragment of a meteorite, typically at the time of recovery. Meteorites are commonly cut, sliced or sometimes broken thus reducing the size of the main mass and the resulting largest specimen is called the "largest known mass". Click on Term to Read More
, courtesy of M. Cimala.
Photo courtesy of Marcin Cimala—Polish Meteorite Laboratory