The assembly of polymict eucrites is neither gentle nor precise. It involves magma, impact excavation and cycles of rock crushing, mixing, lithification and more crushing. Drs. Wittke and Bunch tell us that NWA 2724 contains both subophitic and cumulate textured rock and is therefore polymict. Here is a thin section that shows this nicely. […]
John is a natural history enthusiast living in Oregon.
Five years ago we took a general look at DaG 1040 and last March the subject was its metal content. Recently I got to look at two new thin sections of this meteorite and I am intrigued again by its variety of features and textures. The first five photos below survey the striking difference between […]
NWA 1685 LL4 is a handsome, interesting meteorite. Numerous stones were introduced in two releases by Dean Bessey and called BL. Individuals are glossy black on the outside and clearly brecciated on the inside. The brecciation is distinct because chondritic clasts differ in shock darkening, impact melt rock is featureless grey and many clasts are […]
Tieschitz is interesting in thin section. In our sample, large and small chondrules are set apart by opaque matrix. Radial pyroxene and cryptocrystalline chondrules display aqueous alteration. One large chondrule contains several relict grains. We see chondrules that appear to be radial olivine darkened with fine included particles, probably amphiboles or other alteration products, and […]
Sayh al Uhaymir 008 is one of the several pairings with SaU 005. These pairings have a total weigh of about 25 pounds. It is a Martian basaltic shergottite of a type sometimes called olivine-phyric. It is composed of olivine megacrysts in a finer grained groundmass of pigeonite and plagioclase. In these cross-polarized light (XPL) […]
We’ve seen curtains of microscopic bubbles before in meteorite thin sections. Readers might remember some in Greg Hupé’s NWA 6704 ungrouped achondrite, third photo. Here are others in another ungrouped achondrite that are intriguing for a couple of reasons. They often occur in multiple parallel sheets and they are sometimes quite wavy like heavy drapery. […]
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 […]
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 […]
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 […]
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 […]
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 […]