Chondrites and Chondrules
April 25, 2013
Photographer: Mila Zinkova; Mila's Web site
Summary Author: Mila Zinkova
Chondrites are stony meteorites. They’re the most common and probably the most fascinating type of meteorite. The meteor/meteorite that broke windows in the Russian city of Chelyabinsk this past February was a stony chondrite.
The composition of chondrites is very similar to the composition of the Sun, except that they’re lacking hydrogen and helium. So, if you'd like to hold a piece of the Sun in your palm, chondrites are about as close as you can get. Their name is derived from the chondrules (spherical inclusions) observed in most of them. Chondrules are only found in meteorites. They’re over 4 billion years old -- older than the Earth and other planets. Scientists previously identified meteorites by the crystals found within chondrules, but later they realized that chondrules may recrystallize during weathering processes once they reach the Earth’s surface. Sometimes a broken face of a meteorite is weathered in such a way that 3-D chondrules are seen (above at upper right corner). However, chrondules can be more easily studied by cutting the parent chrondite into slices. Shown at center is a a microscopic image of a 3 cm slice of a chondrite that was found in northwest Africa.
Chrondules are usually small, averaging only about 1 mm in diameter, but almost all chondrites contain bigger ones. Though, rarely is a chondrule 7-8 mm in size found. An example of such a huge chondrule is the green, broken inclusion seen in the middle image. To study crystal structure of a chrondule, polarizing filters and a microscope are required. This approach utilizes thin sections, which are specially prepared slides made so thin that the material can be seen through -- bottom left. More about thin sections of meteorites in an upcoming Earth Science Picture of the Day.