Encore - Chondrite Thin Section

January 05, 2019


Today and every Saturday Earth Science Picture of the Day invites you to rediscover favorites from the past. Saturday posts feature an EPOD that was chosen by viewers like you in our monthly Viewers' Choice polls. Join us as we look back at these intriguing and captivating images.

Mila Zinkova 
Summary Author: Mila Zinkova

Chondrites are perhaps the most interesting of all asteroid fragments. They constitute more than 80 percent of the meteorites observed to fall to Earth and derive their name from the chondrules virtually all of them contain. Chondrules are tiny beads of melted material, often smaller than a rice grain, that actually formed before asteroids took shape early in our solar system's history. Chondrite thin sections examined under a microscope are beautiful to behold – they’re not unlike some of the paintings by Wassily Kandinsky and other abstract artists. Seeing them close up is like discovering a striking new galaxy.

The above image is a thin section of chondrite meteorite NWA4637. I asked Dr. Alan Rubin to describe the image for EPOD readers, and he kindly agreed. He explains: "This is a type-3, L-group ordinary chondrite. The chondrules are well defined; they display a variety of textures and have experienced very little metamorphic heating. At upper left is a large, brown cryptocrystalline chondrule, composed of separate domains of tiny low-calcium pyroxene crystals surrounded by glass. The light-colored rim around the chondrule is a bleached zone altered by the water of the parent asteroid. A smaller porphyritic olivine-pyroxene chondrule is at its lower right. The colorful grains are olivine, the gray grains, are low-calcium pyroxene. To the left of center is a radial pyroxene chondrule made up of low-calcium pyroxene laths arranged in a fan-like array. Part of a barred olivine chondrule can be seen at the extreme right center."

This image represents but a small portion (approximately 1.8 cm by 1 cm) of a single thin section, taken by using a microscope and cross-polarizing filters. The colors of the crystals will change depending on how the filters are rotated, so thin sections of chondrites contain seemingly limitless universes for one to explore.

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