Welcome to the wonderful world of

meteorite Thin Sections

Page updated: March 21, 2014

 

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NWA 5555 - Ureilite

Allende CV3.3

       nwa 5363 - Brachinite

nwa 5797 CM2

    Kapoeta - Howardite

D‘Orbigny - Angrite

  NWA 3305 - Acapulcoite

  Zagami  - Shergottite

NWA 5480 - Olivine diogenite

 A thin section is a laboratory preparation of a meteorite sample for use with a polarizing petrographic microscope. A thin sliver is cut from the meteorite, mounted on a glass slide and then ground to a thickness of only 0.03 mm (= 30 microns). When placed between two polarizing filters, the mineralogy is awash in color which makes it easier to determine the composition of the analysed meteorite, while in transmitted light, thin sections reveal mainly the texture and crystal shape of minerals.


CHONDRITES


Particularly fascinating are the unequilibrated type 3 chondrites.

Chondrites are the largest group of meteorites. They allow us to glimpse the very beginnings of our solar system. The largest structural components of most chondrites are the glass-bearing chondrules, and there are numerous theories for their origin. Here is one:

Chondrules were born in the disk of gas and dust surrounding the young Sun, the same disk that gave rise to the planets. Lightning zaps and shock waves briefly heated isolated regions of the disk, partially melting the dust. The resulting silicate and metal droplets cooled to form the tiny chondrules, which soon collided and stuck together with other minerals to form chondrites.

CARBONACEOUS CHONDRITES

Carbonaceous chondrites are the most primitive and unaltered type of meteorite known. The elemental composition is likely similar to that of the nebula from which the Solar System formed. They contain water or minerals that have been altered in the presence of water, together with large amounts of carbon, including organic compounds.

Only about 5% of all chondrite falls belong to the carbonaceous group. Most carbonaceous chondrites have never been heated above 50°C. They also contain large amounts of olivine and serpentine and a variety of organic compounds, including amino acids (Murchison!)

   DaG 405 - H3.5

  Sahara98035 - LL3

Sahara98035 - LL3

  NWA 3119 - LL4

ACHONDRITES

Achondrites are the rarer of the two main types of stony meteorites. Only about 9% of all meteorite falls are achondrites, that means, they do not contain chondrules. Achondrites are made of rock that has crystallized from a molten state, material similar to terrestrial basalts or plutonic rocks that have been differentiated and reprocessed to a lesser or greater degree. Due to melting and recrystallization on or inside meteorite parent bodies. They contain mostly one or more of the minerals plagioclase, pyroxene, and olivine. Most achondrites are chemically similar to basalts and are thought to be the product of melting on large asteroids, moons, and planets. Soon after these worlds formed, they were partially melted: This process is still active on Earth, but it ended about 4.4 billion years ago on asteroids, that means relatively shortly after the formation of our solar system.

Under crossed polarized light (XPL), many of these achondrites are very colorful, especially primitive achondrites like ureilites, lodranites, brachinites and acapulcoites.