Dar al Gani 1040 is from central Libya, found on a long limestone plateau at about 2,000 feet elevation. We’ve looked at DaG 1040 before and noted its friable matrix, varied chondrules and prominent metal. Here we’ll concentrate on the metal. All photos, except the first two, are of thin sections in incident light.
Amoeboid olivine aggregates are common millimeter size inclusions in carbonaceous chondrite meteorites. Some are amoeba shaped, some are more chondrule-like. Their textures and compositions are variable, too – some appear to be transitional between calcium-aluminum-rich inclusions and some transitional between chondrules. The olivine is the magnesium-rich end member, forsterite. It was formed not from a melt of precursor dust but
3.00 is a rarely given petrologic grade assigned to meteorites which experienced the lowest levels of thermal alteration on the parent body. (Aqueous alteration is another matter.) NWA 8276 L3.00 was assigned this grade based on laboratory tests and a study by Grossman and Brearley published in 2005. Among many findings the study’s authors showed that at the onset of
About 1% of the volume of NWA 869 L3-6 is impact melt rock (IMR) according to Metzler et al. Their study tells us a lot about these highly variable fine grained inclusions we find in cut stones. Some IMR clasts include mineral and rock clasts, some do not. The crystallized fallback material is depleted in nickel-iron metal and sulfides. Grains
It’s a harsh place, the surface of the moon. NWA 8010 is a lunar regolith breccia meteorite that bears witness to this. Melt veins are formed by large impacts. The veins in NWA 8010 did not cool instantly into glass. They had time to nucleate along wall rock and crystallize into feathery tufts of very fine laths that grew to
The outer portion of some olivine grains in the Moss meteorites have levels of iron elevated above those in the center of the grains. This difference can be seen in some grains that have been thin sectioned. These photos are all of one rather small sample. All photos are in cross-polarized transmitted light.
The wavy black forms signal a symplectitic texture. Symplectites appear in metals, minerals and other materials. They are intergrowths of two or more constituents and appear in a variety of configurations. They may be considered a disequilibrium textural feature. The different phases may form from: a single phase that becomes unstable from a pressure or temperature change (e.g. exsolution); a
This is a selection of photos of various thin sections in the horde released by Arizona State University earlier this year. Most are at a higher magnification than those I usually place here.
The Selma meteorite was found near that Alabama city in 1906. At 310 pounds it was then the largest meteorite found in the United States. It was purchased by the American Museum of Natural History (New York). The thin section pictured here was deaccessioned by Arizona State University in early 2014 and is now in a private collection in France.
Earlier this year Arizona State University released about a hundred surplus thin sections. This was through a trade with meteorite dealer Anne Black. I bought a few of these slides from her. I chose the only Romero H4 she had because it had an inclusion. The write up in the Meteoritical Bulletin Database gives only basic information on Romero so
These photos were taken of four thin sections that were deaccessioned by a US university. They appear to have been made by different people and at different times. On one, the cover slip cement has turned yellow. Some have labeling engraved on the slide behind the sample. Some of this can be attributed to the sample size being very large,
These chondrules show the effects of multiple heating events coupled with accretion. They are chondrules and mineral grains that have gathered nebular dust, been heated and ended up with porphyritic olivine and pyroxene jackets.
In thin section under the microscope it is easy to see that the components of Dhofar 008 L3.3 underwent several episodes of processing before their final assembly and delivery to earth. We see it in layered features and in the presence of enveloping compound chondrules. Enveloping compound chondrules have one or more chondrules completely enclosed in another. With enveloping compound
Ibitira is the exception that nags us when we introduce people to the appearance of meteorites versus meteor wrongs. We like to say that if it has bubbles it isn’t the real thing, thus dismissing slag, lava and their cousins. But Ibitira and a few other exceptional meteorites do have vesicles. Ibitira is exceptional also in that it is a
