Archive - Thin Section of Allende Meteorite

July 28, 2019

ZZZMicroscopic view of Meteorite thin section Allende

Each Sunday we present a notable item from our archives. This EPOD was originally published July 28, 2013.

Photographer: Mila Zinkova
Summary Author: Mila Zinkova

This image shows a thin section of a piece of the Allende meteorite that fell to the ground in Mexico on February 8, 1969. The photo was taken through a light microscope using cross-polarized illumination. Allende is a carbonaceous chondrite meteorite notable for its calcium-aluminum-rich inclusions (CAI). It’s one of the oldest objects in the Solar system. This kind of meteorite is older than chondrules and even older than the Earth itself.

According to Dr. Alan Rubin, Allende is an oxidized CV3 carbonaceous chondrite that, like other unmetamorphosed chondrites, contains material that was likely derived from supernovas. The large irregular brown inclusions here are amoeboid olivine aggregates (AOIs), composed mainly of small olivine grains (forsterite). The colorful spheroid and ellipsoidal objects that look like stained glass are porphyritic chondrules made up of relatively coarse olivine and low-Ca pyroxene grains. A blackened region that surrounds the chondrules and inclusions is the meteorite matrix. With the Allende meteorite, the matrix consists of elongated olivine grains, moderate amounts of sulfide, minor amounts of magnetite, and even small amounts of clay minerals.

The original Allende stone was thought to be an automobile-sized object as it neared the Earth's surface over the Mexican state of Chihuahua. It exploded before striking the ground, thus there was no impact crater.