Amphoterite is an obsolete classification of chondriticmeteorites that are now classified as LL (Low Iron and Low total metal content) types.
Chondrites are stony (non-metallic) meteorites that have not been modified due to melting or differentiation of the parent body. They are formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids. They are the most common type of meteorite that falls to Earth with estimates for the proportion of the total fall that they represent varying between 85.7% and 86.2%. Their study provides important clues for understanding the origin and age of the Solar System, the synthesis of organic compounds, the origin of life and the presence of water on Earth. One of their characteristics is the presence of chondrules, which are round grains formed by distinct minerals, that normally constitute between 20% and 80% of a chondrite by volume.
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the object enters the atmosphere, various factors such as friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate that energy. It then becomes a meteor and forms a fireball, also known as a shooting star or falling star; astronomers call the brightest examples "bolides". Meteorites vary greatly in size. For geologists, a bolide is a meteorite large enough to create an impact crater.
The LL chondrites are a group of stony meteorites, the least abundant group of the ordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively. The composition of the Chelyabinsk meteor is that of a LL chondrite meteorite. The material makeup of Itokawa, the asteroid visited by the Hayabusa spacecraft which landed on it and brought particles back to Earth also proved to be type LL chondrite.
Most of the iron in these types of meteorites is present as ironoxide in the minerals (e.g. olivine) rather than as free metal, as it is found in most other meteorites. Free metallic iron amounts to between 0.3% and 3.0% of the meteorite, and with a total iron content of 20% give or take a couple of percentage points.
Iron is a chemical element with symbol Fe and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space.
A mineral is, broadly speaking, a solid chemical compound that occurs naturally in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are usually excluded, but some minerals are often biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings often syntesize inorganic minerals that also occur in rocks.
The mineral olivine is a magnesium iron silicate with the formula (Mg2+, Fe2+)2SiO4. Thus it is a type of nesosilicate or orthosilicate. It is a common mineral in Earth's subsurface but weathers quickly on the surface.
There will be a number after the LL in a meteorites classification type, e.g. LL3, LL5, LL6. (Types range from 3 to 7) The number indicates the amount of alteration suffered by the chondrules in the meteorite.
A Chondrule is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids. Because chondrites represent one of the oldest solid materials within the Solar System and are believed to be the building blocks of the planetary system, it follows that an understanding of the formation of chondrules is important to understand the initial development of the planetary system.
A chondrule is a small mineral ball generally 0.1–4 millimetres (0.0039–0.1575in) in diameter. An LL3 type is pristine with perfectly discernible chondrules, an LL7 type has been melted or altered by pressure or other force to almost completely obliterate the round chondrules.
Melting, or fusion, is a physical process that results in the phase transition of a substance from a solid to a liquid. This occurs when the internal energy of the solid increases, typically by the application of heat or pressure, which increases the substance's temperature to the melting point. At the melting point, the ordering of ions or molecules in the solid breaks down to a less ordered state, and the solid melts to become a liquid.
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure.
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Kamacite is an alloy of iron and nickel, which is found on Earth only in meteorites. The proportion iron:nickel is between 90:10 and 95:5; small quantities of other elements, such as cobalt or carbon may also be present. The mineral has a metallic luster, is gray and has no clear cleavage although its crystal structure is isometric-hexoctahedral. Its density is about 8 g/cm3 and its hardness is 4 on the Mohs scale. It is also sometimes called balkeneisen.
The ultimate goal of meteorite classification is to group all meteorite specimens that share a common origin on a single, identifiable parent body. This could be a planet, asteroid, Moon, or other current Solar System object, or one that existed some time in the past. However, with a few exceptions, this goal is beyond the reach of current science, mostly because there is inadequate information about the nature of most Solar System bodies to achieve such a classification. Instead, modern meteorite classification relies on placing specimens into "groups" in which all members share certain key physical, chemical, isotopic, and mineralogical properties consistent with a common origin on a single parent body, even if that body is unidentified. Several meteorite groups classified this way may come from a single, heterogeneous parent body or a single group may contain members that came from a variety of very similar but distinct parent bodies. As such information comes to light, the classification system will most likely evolve.
C-type (carbonaceous) asteroids are the most common variety, forming around 75% of known asteroids. They are distinguished by a very low albedo because their composition includes a large amount of carbon, in addition to rocks and minerals. They occur most frequently at the outer edge of the asteroid belt, 3.5 astronomical units (AU) from the Sun, where 80% of the asteroids are of this type, whereas only 40% of asteroids at 2 AU from the Sun are C-type. The proportion of C-types may actually be greater than this, because C-types are much darker than most other asteroid types except for D-types and others that are mostly at the extreme outer edge of the asteroid belt.
A micrometeorite is essentially a micrometeoroid that has survived entry through Earth's atmosphere. The size of such a particle ranges from 50 µm to 2 mm. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. They are a subset of cosmic dust, which also includes the smaller interplanetary dust particles (IDPs).
Enstatite is a mineral; the magnesium endmember of the pyroxene silicate mineral series enstatite (MgSiO3) - ferrosilite (FeSiO3). The magnesium rich members of the solid solution series are common rock-forming minerals found in igneous and metamorphic rocks. The intermediate composition, (Mg,Fe)SiO3, has historically been known as hypersthene, although this name has been formally abandoned and replaced by orthopyroxene. When determined petrographically or chemically the composition is given as relative proportions of enstatite (En) and ferrosilite (Fs) (e.g., En80Fs20).
Carbonaceous chondrites or C chondrites are a class of chondritic meteorites comprising at least 8 known groups and many ungrouped meteorites. They include some of the most primitive known meteorites. The C chondrites represent only a small proportion (4.6%) of meteorite falls.
Ataxites are a structural class of iron meteorites with a high nickel content and show no Widmanstätten patterns upon etching.
Iron meteorites are meteorites that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Iron meteorites originate from cores of planetesimals.
The ordinary chondrites are a class of stony chondritic meteorites. They are by far the most numerous group and comprise about 87% of all finds. Hence, they have been dubbed "ordinary". The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively.
The L type ordinary chondrites are the second most common group of meteorites, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively.
The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After breaking up in the atmosphere, an extensive search for pieces was conducted and over 2 tonnes (tons) of meteorite were recovered. The availability of large quantities of samples of the scientifically-important chondrite class has enabled numerous investigations by a large number of scientists; it is often described as "the best-studied meteorite in history." The Allende meteorite has abundant, large calcium-aluminium-rich inclusions, which are among the oldest objects formed in the Solar System.
Pultusk is an H5 ordinary chondrite meteorite which fell on 30 January 1868 in Poland. The event has been known as the stony meteorite shower with the largest number of pieces yet recorded in history. Made up of rocky debris, it consists of pyroxene or olivine chondrules deployed in mass plagioclase, there being also kamacite.
Enstatite chondrites are a rare form of meteorite thought to comprise only about 2% of the chondrites that fall on Earth. Only about 200 E-Type chondrites are currently known.
CI chondrites, sometimes C1 chondrites, are a group of rare stony meteorites belonging to the carbonaceous chondrites. Samples have been discovered in France, Canada, India, and Tanzania. Compared to all the meteorites found so far, their chemical composition most closely resembles the elemental distribution in the sun's photosphere.
Winonaites are a group of primitive achondrite meteorites. Like all primitive achondrites, winonaites share similarities with chondrites and achondrites. They show signs of metamorphism, partial melting, brecciation and relic chondrules. Their chemical and mineralogical composition lies between H and E chondrites.
The Zakłodzie meteorite is a stony-iron meteorite found in Poland in 1998. Its mass is 8.68 kilograms (19.1 lb). It is composed predominantly from enstatite and meteoric iron. Currently classified as an ungrouped enstatite achondrite its classification is still an ongoing scientific debate.
This is a glossary of terms used in meteoritics, the science of meteorites.
