![]() ![]() They are a mechanical mixture of components that formed in the solar nebula or even earlier. In terms of terrestrial rocks, these meteorites seem akin to sedimentary conglomerates-i.e., fragments of preexisting rock cemented together. They also are arguably the most important. Chondrites have been subdivided into three main classes- ordinary, carbonaceous, and enstatite chondrites-and these in turn have been divided into a number of groups.Ĭhondrites are the most abundant meteorites (about 87 percent of stony meteorites) in collections. The most fundamental distinction between the various stony meteorites is between those that were once molten, the achondrites, and those that were not, the chondrites. Thus, the challenge for researchers is to determine which types of meteorites are related and which are not, as well as to identify the processes that were responsible for the tremendous diversity that is seen among them. When the differentiated asteroid is later broken up by collisions, samples of its rocky mantle, iron core, and core-mantle interface might be represented in the three main categories. This separation process is known as geochemical differentiation. For instance, if a large asteroid were to melt, its denser metallic components would tend to sink to its centre (its core), while its less-dense rocky material would form a mantle around it, much like what happened to Earth. Conversely, subdivisions from different categories may have a common origin. Indeed, more often than not, they are unrelated. Just because subdivisions belong to the same category, it does not necessarily follow that they all consist of meteorites that have the same or similar parent bodies. It is important to realize that meteorite classification is based primarily on observable characteristics. There is considerable diversity within each category, leading to numerous subdivisions (classes, groups, etc.) based on variations in chemistry, mineralogy, and structure. ![]() Stony meteorites make up about 94 percent of all known meteorites, irons about 5 percent, and stony irons about 1 percent. Meteorites traditionally have been divided into three broad categories- stony meteorites (or stones), iron meteorites (irons), and stony iron meteorites (stony irons)-on the basis of the proportions of rock-forming minerals and nickel-iron (also called iron-nickel) metal alloy they contain. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century.100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions. ![]()
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