A chondrule is a roughly spherical aggregate of coarse crystals formed from the rapid cooling
and solidification of a melt at about 1400°C. Large numbers of chondrules
are found in all chondrites except for
the CI group of carbonaceous chondrites. Chondrules
are typically 0.5 to 2mm in diameter and are usually composed of iron, aluminum,
or magnesium silicates in the form of the minerals olivine and pyroxene, with smaller amounts of glass and iron-nickel.
Together with calcium aluminium
inclusions, which predate them by a couple of million years, they are
among the oldest objects in the Solar System with an age of about 4.57 billion
years. They formed when dusty regions of the solar
nebula were heated to very high temperatures, became molten, and then
resolidified as tiny droplets.
|Cross-section of a chondrule in a small H5 chondrite
found in about 1960 in Riverton, Manitoba