These chondrules from the Greek for small sphere formed 4. Chondrules are not found in terrestrial rocks. These chondrules, along with small mineral grains, accreted to form asteroids during the birth of the Solar System.
Chondrites are, by far, the most abundant type of stony meteorite. Less common, comprising only a few percent of all meteorites, are achondrites. These are also stony meteorites composed primarily of silicates, but these meteorites have experienced familiar geologic processes of melting and differentiation - although these happened long ago. Most achondrites formed on asteroids during the birth of the Solar System, but a small number formed on Mars and the Moon.
Stony-iron meteorites form in places where metal and silicate are mixed. One type of stony-iron are pallasites - rocks composed of a network of iron-nickel metal surrounding a greenish, silicate mineral called olivine. Pallasites probably form when the olivine-rich mantle of an asteroid mixes with the metallic core. Mesosiderites are mixtures of iron-nickel metal and basalt and probably formed by the collision of two asteroids.
They are pieces of the cores of asteroids. Early in Solar System history, asteroids melted and the dense iron-nickel metal sank to the center to form a core - much like the Earth has a core. Iron meteorites are the samples of the cores of ancient worlds. While they are rare among meteorites seen to fall to Earth only a few percent , they are among the most common type of meteorites in our collections, because they can be recognized long after their fall, are very different from Earth rocks, and are resistant to weathering.
Take your classroom into the great beyond with these out-of-this-world resources. Fewer than meteorites have been traced to the planet Mars, one of our closest neighbors in the solar system. Learn more about them here. Meteoroids are lumps of rock or iron that orbit the sun, just as planets, asteroids, and comets do. Meteoroids, especially the tiny particles called micrometeoroids, are extremely common throughout the solar system.
They orbit the sun among the rocky inner planets, as well as the gas giants that make up the outer planets. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. Meteorites are the last stage in the existence of these type of space rocks. Before they were meteorites, the rocks were meteor s.
Before they were meteors, they were meteoroid s. Meteoroids are lumps of rock or metal that orbit the sun. Some meteorites, however, are as large as boulder s. The largest meteorite found on Earth is the Hoba meteorite discover ed in Namibia in The Hoba meteorite weighs roughly 54, kilograms , pounds.
The Hoba meteorite is so big, and so heavy, it has never been moved from where it was found! Most meteorites look very much like rocks found on Earth, except meteorites usually have a dark, burned exterior. This exterior is formed as friction from the atmosphere melts the meteorite as it crashes toward Earth. Known as thermal ablation , this process can also give meteorites a roughened, smooth, or thumbprint surface. Thermal ablation creates these different texture s due to different chemicals present in the meteorite.
Meteorites crash through the atmospheres of all planet s and moon s in our solar system. Some planets and moons don't have enough atmosphere to break apart meteors, resulting in large meteorites. These larger meteorites create deep, round impact crater s that can be found all over our Moon, Mercury, and Mars. More than 60, meteorites have been found on Earth. Scientists have divided these meteorites into three main types: stony, iron, and stony-iron.
Each of these types has many sub-groups. Stony meteorite s are made up of mineral s that contain silicate s—material made of silicon and oxygen.
They also contain some metal—nickel and iron. There are two major types of stony meteorites: chondrites and achondrites. Chondrite s themselves are classified into two major groups: ordinary and carbonaceous.
Ordinary chondrites are the most common type of stony meteorite, accounting for 86 percent of all meteorites that have fallen to Earth. They are named for the hardened droplets of lava , called chondrule s, embed ded in them. Chondrites formed from the dust and small particle s that came together to form asteroid s in the early solar system, more than 4.
Ordinary chondrites can be classified into three main groups. The H chondrite group has a h igh amount of iron. The L chondrite group has a l ow amount of iron. The LL group has a l ow amount of iron and a l ow amount of metal in general. Carbonaceous chondrite s are much more rare than ordinary chondrites.
Astronomer s think carbonaceous chondrites formed far away from the sun as the early solar system developed. As their name implies, carbonaceous chondrites contain the element carbon, usually in the form of organic compound s such as amino acid s. Carbonaceous chondrites also often contain water or material that was shaped by the presence of water.
Like ordinary chondrites, carbonaceous chondrites can be more minute ly classified based on their mineral composition. The meteorite , which was discovered in the Sahara desert in , dates from just 2 million years after the formation of the solar system — making it more than a million years older than the previous record-holder.
When he and his colleagues analysed the meteorite, called Erg Chech or EC , they found that it was unlike any other meteorite we have ever located. It is a type of rock called andesite that, on Earth, is found mostly in subduction zones — areas where tectonic plates have collided and one has been pushed beneath the other — and rarely in meteorites.
Most of the meteorites discovered on Earth are made of another kind of volcanic rock called basalt.
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