Meteorites consist of the same chemical elements, which also exist on Earth.
Basically there are 8 elements: iron, nickel, magnesium, sulfur, aluminum, silicon, calcium, oxygen. Other elements are also found in meteorites, but in very small quantities. The constituent elements interact with each other to form various minerals in meteorites. Most of them are also present on Earth. But there are meteorites with minerals unknown on earth.
Meteorites are classified according to their composition as follows:
stone(Most of them chondrites, because contain chondrules- spherical or elliptical formations of predominantly silicate composition);
iron-stone;
iron.
Iron meteorites consist almost entirely of iron combined with nickel and a small amount of cobalt.
Rocky meteorites contain silicates - minerals that are a compound of silicon with oxygen and admixtures of aluminum, calcium and other elements. IN stone In meteorites, nickel iron is found in the form of grains in the meteorite mass. Iron-stone meteorites consist mainly of equal amounts of stony material and nickel iron.
Found in different places on Earth tektites– small glass pieces of a few grams. But it has already been proven that tektites are frozen terrestrial matter ejected during the formation of meteorite craters.
Scientists have proven that meteorites are fragments of asteroids (minor planets). They collide with each other and break into smaller fragments. These fragments fall to Earth in the form of meteorites.
Why do we study the composition of meteorites?
This study provides insight into the composition, structure and physical properties other celestial bodies: asteroids, planetary satellites, etc.
Traces of extraterrestrial organic matter have also been found in meteorites. Carbonaceous (carbonaceous) meteorites have one important feature- the presence of a thin glassy crust, apparently formed under the influence of high temperatures. This crust is a good heat insulator, thanks to which minerals that cannot withstand strong heat, such as gypsum, are preserved inside carbonaceous meteorites. What does it mean? This means that when studying the chemical nature of such meteorites, substances were discovered in their composition that, under modern earthly conditions, are organic compounds of a biogenic nature. I would like to hope that this fact indicates the existence of life outside the Earth. But, unfortunately, it is impossible to speak about this clearly and with confidence, because theoretically, these substances could also be synthesized abiogenically. Although it can be assumed that if the substances found in meteorites are not products of life, then they may be products of pre-life - similar to that which once existed on Earth.
When researching stony meteorites even so-called “organized elements” are found - microscopic (5-50 microns) “unicellular” formations, often having clearly defined double walls, pores, spines, etc.
Meteorite falls are impossible to predict. Therefore it is unknown where and when meteorite will fall. For this reason, only a small part of the meteorites that fall to Earth ends up in the hands of researchers. Only 1/3 of the fallen meteorites were observed during the fall. The rest are random finds. Of these, most are iron ones, as they last longer. Let's talk about one of them.
Sikhote-Alin meteorite
He fell in the Ussuri taiga in the Sikhote-Alin mountains on Far East On February 12, 1947, at 10:38 a.m., it fragmented in the atmosphere and fell as iron rain over an area of 35 square kilometers. Parts of the rain were scattered across the taiga over an area in the form of an ellipse with an axis about 10 kilometers long. In the head part of the ellipse (crater field) 106 craters were discovered, with a diameter from 1 to 28 meters, the depth of the largest crater reached 6 meters.
According to chemical analyses, the Sikhote-Alin meteorite is classified as iron: it consists of 94% iron, 5.5% nickel, 0.38% cobalt and small amounts of carbon, chlorine, phosphorus and sulfur.
The first to discover the site of the meteorite fall were the pilots of the Far Eastern Geological Department, who were returning from a mission.
In April 1947, to study the fall and collect all parts of the meteorite, the Committee on Meteorites of the USSR Academy of Sciences organized an expedition led by Academician V. G. Fesenkov.
Now this meteorite is in the meteorite collection of the Russian Academy of Sciences.
How to recognize a meteorite?
Almost most meteorites are found by accident. How can you determine that what you found is a meteorite? Here are the simplest signs of meteorites.
They have high density. They are heavier than granite or sedimentary rocks.
The surface of meteorites often shows smooth depressions, like finger indentations in clay.
Sometimes a meteorite looks like a blunted projectile head.
Fresh meteorites show a thin melting crust (about 1 mm).
The fracture of a meteorite is most often gray in color, on which small balls - chondrules - are sometimes visible.
In most meteorites, inclusions of iron are visible in the cross-section.
Meteorites are magnetized, the compass needle deviates noticeably.
Over time, meteorites oxidize in air, acquiring a rusty color.
Meteorites, super category of finds with a metal detector. Expensive and regularly replenished. The only problem is how to distinguish a meteorite... Finds that look like a stone and give a metal detector response are not uncommon in the mine. At first I tried to rub it on the blade of a shovel, but over time I collected in my head the characteristic differences between celestial meteorites and earthly meteorites.
How to distinguish a meteorite from an artifact of terrestrial origin. Plus photos from the search engine forum, finds of meteorites and similar ones.
The good news is that 5000-6000 kilograms of meteorites fall to the ground in 24 hours. It’s a pity that most of them go under water, but there are plenty of them in the ground.
How to distinguish a meteorite
Two important properties. A meteorite never has an internal horizontal structure(layers). The meteorite is not like a river stone.
Melted surface. If there is one, this is a good sign. But if the meteorite lay in the ground or on the surface, the surface may lose its glaze (by the way, it is most often thin, 1-2 mm).
Form. A meteorite can have any shape, even square. But if it is a regular ball or sphere, most likely it is not a meteorite.
Magnetic. Almost all meteorites (about 90%) stick to any magnet. But the earth is full of natural stones that have the same properties. If you see that it is metal and it does not stick to a magnet, it is highly likely that this find is of terrestrial origin.
Appearance. 99% of meteorites do not have quartz inclusions and there are no “bubbles” in them. But there is often a grain structure. A good sign is “plastic indentations”, something like fingerprints in plasticine (the scientific name for such a surface is Regmaglypts). Meteorites most often contain iron, which, once on the ground, begins to oxidize; it looks like a rusty stone))
Photos of finds
There are plenty of photos of meteorites on the Internet... I'm only interested in those that were found with a metal detector ordinary people. They found it and doubt whether it is a meteorite or not. Forum thread (bourgeois).
The usual advice from experts goes something like this... Pay attention to the surface of this stone - the surface will definitely have indentations. A real meteorite flies through the atmosphere, while it heats up very much and its surface “boils”. The upper layers of meteorites always retain traces high temperature. Characteristic dents similar to burst bubbles - first characteristic feature meteorite
You can try the stone on magnetic properties. Simply put, bring a magnet to it and move it over it. Find out if the magnet sticks to your stone. If the magnet sticks, then there is a suspicion that you have actually become the owner of a piece of a real celestial body. This type of meteorite is called iron meteorite. It happens that a meteorite is not very magnetic, only in some fragments. Then it might be a stony-iron meteorite.
There is also a type of meteorite - stone. It is possible to detect them, but it is difficult to determine that it is a meteorite. You can't do without it here chemical analysis. A special feature of meteorites is the presence of rare earth metals. And there is also a fusion bark on it. Therefore, the meteorite is usually very dark in color. But there are also whitish ones.
Debris that lies on the surface is not considered subsoil. You are not breaking any laws. The only thing that may sometimes be required is to obtain an opinion from the Committee on Meteorites of the Academy of Sciences; they must conduct research and assign a class to the meteorite. But this is the case if the find is very impressive, and it is difficult to sell it without a conclusion.
At the same time, to claim that the search and sale of meteorites is crazy profitable business, it is forbidden. Meteorites are not bread, there are no queues for them. You can sell a piece of the “sky wanderer” abroad for a better profit.
Exist certain rules for the removal of meteorite matter. First you need to write an application to Okhrankultura. There you will be sent to an expert who will write a report on whether the stone can be removed. Usually, if it is a registered meteorite, there are no problems. You pay a state duty - 5-10% of the cost of the meteorite. And forward to foreign collectors.
Instructions
All meteorites are divided into iron, stony-iron and stone, depending on their chemical composition. The first and second have a significant percentage of nickel content. They are found infrequently, because having a gray or brown surface, they are indistinguishable by eye from ordinary stones. The best way to look for them is with a mine detector. However, when you pick one up, you will immediately realize that you are holding metal or something similar to it.
Iron meteorites have high specific gravity and magnetic properties. Fallen long ago, they acquire a rusty tint - this is theirs. distinctive feature. Most of Ironstone and stony meteorites are also magnetized. The latter, however, are significantly less. It is quite easy to detect a recently fallen one, since a crater usually forms around the place where it fell.
As the meteorite moves through the atmosphere, it becomes very hot. In those who recently fell, a melted shell is noticeable. After cooling, regmaglypts remain on their surface - depressions and protrusions, as if from fingers, and fur - traces reminiscent of burst bubbles. Meteorites are often shaped like a slightly rounded head.
Sources:
- Committee on Meteorites of the Russian Academy of Sciences
– celestial stones or pieces of metal flying from space. They are quite inconspicuous in appearance: gray, brown or black. But meteorites are the only extraterrestrial substance that can be studied or at least held in one's hands. With their help, astronomers learn the history of space objects.
You will need
- Magnet.
Instructions
The simplest, but also the best indicator that the average person can get is a magnet. All sky stones contain iron, which... A good option- such an object in the form of a horseshoe with four pounds of tension.
After such initial testing, the possible one should be sent to the laboratory to confirm or refute the authenticity of the find. Sometimes these tests last about a month. Cosmic rocks and their terrestrial brothers are composed of the same minerals. They differ only in the concentration, combination and mechanics of the formation of these substances.
If you think that what you have in your hands is not a ferrous meteorite, but a meteorite, testing with a magnet will be pointless. Examine it carefully. Rub your find thoroughly, focusing on a small area about the size of a coin. This way you will make it easier for yourself to study the stone matrix.
They have small spherical inclusions that resemble freckle spots of solar iron. This is a distinctive feature of “traveler” stones. This effect cannot be produced artificially.
Video on the topic
Sources:
- The shape and surface of meteorites. in 2019
The meteorite can be distinguished from an ordinary stone right at the place of discovery. According to the law, a meteorite is considered a treasure and the finder receives a reward. Instead of a meteorite, there may be other natural wonders: a geode or an iron nugget, even more valuable.
This article tells you how to determine right at the place of discovery whether it is a simple cobblestone, a meteorite or another natural rarity mentioned later in the text. Equipment and tools you will need are paper, a pencil, a strong (at least 8x) magnifying glass and a compass; preferably - good camera and GSM navigator. Also - a small garden or sapper. No chemicals or a hammer and chisel are required, but a plastic bag and soft packaging material are required.
What is the essence of the method
Meteorites and their “simulators” have enormous scientific value and are considered treasures by Russian legislation. The finder, after evaluation by experts, receives a reward.
However, if the find was subjected to chemical, mechanical, thermal and other unauthorized influences before being delivered to a scientific institution, its value decreases sharply, several times or tens of times. For scientists higher value may have the rarest sinter minerals on the surface of the sample and its interior preserved in its original form.
Treasure hunters-“predators”, who independently clean their finds to a “marketable” state and break them into souvenirs, not only harm science, but also greatly deprive themselves. Therefore, it is further described that there is over 95% confidence in the value of what was discovered, without even touching it.
External signs
Meteorites fly into the earth's atmosphere at a speed of 11-72 km/s. At the same time, they melt. The first sign of the extraterrestrial origin of the find is the melting crust, which differs in color and texture from the interior. But in iron, iron-stone and stone meteorites different types melting crust is different.
Small iron meteorites entirely take on a streamlined or ogival shape, somewhat reminiscent of a bullet or artillery shell (item 1 in the figure). In any case, the surface of the suspicious “stone” is smoothed, as if sculpted from, pos. 2. If the sample also has a bizarre shape (item 3), then it may turn out to be both a meteorite and a piece of native iron, which is even more valuable.
Fresh melting bark is blue-black (Pos. 1,2,3,7,9). In an iron meteorite that has lain in the ground for a long time, it oxidizes over time and changes color (Pos. 4 and 5), and in an iron-stone meteorite it can become similar to ordinary rust (Pos. 6). This often misleads seekers, especially since the melting relief of a stony-iron meteorite that flew into the atmosphere at a speed close to the minimum can be poorly expressed (Pos. 6).
In this case, a compass will help out. Bring it to, if the arrow points to a “stone”, then it is most likely an iron-containing meteorite. Iron nuggets are also “magnetic”, but they are extremely rare and do not rust at all.
In stony and stony-iron meteorites, the melting crust is heterogeneous, but in its fragments some elongation in one direction is already visible to the naked eye (Pos. 7). Rocky meteorites often break up while still in flight. If the destruction occurred in the final section of the trajectory, their fragments, which do not have a melting crust, may fall to the ground. However, in this case, their internal structure is exposed, which is not similar to any earthly minerals (Pos. 8).
If a sample is chipped, then in mid-latitudes you can determine whether it is a meteorite or not at first glance: the melting crust is sharply different from the interior (Pos. 9). It will accurately show the origin of the bark under a magnifying glass: if a streaky pattern is visible on the bark (Pos. 10), and so-called organized elements are visible on the chip (Pos. 11), then this is most likely a meteorite.
In the desert, the so-called stone tan can be misleading. Also in deserts, wind and temperature erosion are strong, which is why the edges of ordinary stone can be smoothed out. In a meteorite, the influence of the desert climate can smooth out the streaky pattern, and the desert tan can tighten the chip.
In the tropical zone, external influences on rocks are so strong that meteorites on the ground surface soon become difficult to distinguish from simple stones. In such cases, approximate specific gravity after removal from the deposit can help to gain confidence in the find.
Documentation and seizure
In order for a find to retain its value, its location before removal must be documented. For this:
· Via GSM, if you have a navigator, and record geographical coordinates.
· We take pictures with different sides from far and near (from different angles, as photographers say), trying to capture in the frame everything remarkable near the sample. For scale, next to the find we place a ruler or an object of known size (lens cap, matchbox, tin can, etc.)
· We draw croques (plan diagram of the find site without scale), indicating compass azimuths to the nearest landmarks ( settlements, geodetic signs, noticeable hills, etc.), with an eye assessment of the distance to them.
Now you can start withdrawing. First, we dig a trench on the side of the “stone” and watch how the type of soil changes along its length. The find must be removed along with the deposits around it, and in any case, in a soil layer of at least 20 mm. Scientists often value the chemical changes around a meteorite more than the meteorite itself.
Having carefully dug up, we put the sample in a bag and estimate its weight with our hands. Light elements and volatile compounds are “swept out” of meteorites in space, so their specific gravity is greater than that of terrestrial rocks. For comparison, you can dig up and weigh a similar-sized cobblestone in your hands. The meteorite, even in a layer of soil, will be much heavier.
What if it’s a geode?
Meteorites that have lain in the ground for a long time are often similar in appearance to geodes - crystallization “nests” in the earth’s rocks. The geode is hollow, so it will be lighter than even an ordinary stone. But don't be disappointed: you're just as lucky. Inside the geode is a nest of natural piezoquartz, and often precious stones(Pos. 12). Therefore, geodes (and iron nuggets) are also considered treasures.
But under no circumstances should you split the object into a geode. In addition to the fact that it will depreciate significantly, the illegal sale of gems entails criminal liability. The geode must be taken to the same facility as the meteorite. If its contents have jewelry value, the finder, by law, has the right to an appropriate reward.
Where to take it?
The find must be delivered to the nearest scientific institution, at least to a museum. You can also go to the police; the regulations of the Ministry of Internal Affairs provide for such a case. If the find is too heavy, or the scientists and the police are not very far away, it is better not to seize it at all, but to call one or the other. This does not detract from the rights of the finder and the reward, but the value of the find increases.
If you still have to transport it yourself, the sample must be provided with a label. In it you need to indicate the exact time and place of discovery, all significant, in your opinion, circumstances of the discovery, your full name, time and place of birth and permanent residence address. Crocs and, if possible, photographs are attached to the label. If the camera is digital, then the files from it are downloaded to the media without any processing, preferably in addition to the computer, directly from the camera to a flash drive.
For transportation, the sample in a bag is wrapped in cotton wool, synthetic padding or other soft padding. It is also advisable to place it in a strong wooden box, securing it from shifting during transportation. In any case, you need to deliver it yourself only to a place where qualified specialists can arrive.
These are the most common meteorites; they consist mainly of silicates, sometimes with admixtures of carbon and traces of iron. If we accept as a hypothesis that the low oxidation state of these meteorites depends on the location where they formed, meaning how far away from the Sun their parent proto-bodies were at the time of their formation, then we can classify them from lowest to highest oxidation as follows:
- Enstatite chondrites (E): they are divided into two subgroups H and L, depending on the iron content; less than 12% for the L-group and above 35% for the H-group. They consist mainly of pyroxene and may also contain some silicates (tridymite). They were heated to temperatures above 650ºС, and in collections they are coded with the letter E.
- Ordinary chondrites (OC): They make up 80% of all chondrites and are divided into 3 subgroups according to their iron content:
- group H: consist of olivine, pyroxene (bronzite) and 12-21% free iron,
- group L: consist of olivine, pyroxene (hypersthene) and 7-12% free iron,
- group LL: from 35% olivine and very little free iron, always less than 7%.
- Carbonaceous chondrites: these are the most primitive of all chondrites, in composition they are very close to the gas and dust cloud from which they formed solar system. They consist mainly of 40% olivine, 30% pyroxene and some carbon, sometimes in the form organic compounds. However, they contain very little or no iron. This is a rather heterogeneous group, studied and divided into 4 subgroups by scientists Van Schmutz and Haynes in 1974:
- CO, Ornance type (France): contains 0.2% to 1.0% carbon and about 1.0% water, chondrules are very small.
- CV, Vigarano type (Italy): contains less than 0.2% carbon and less than 0.03% water. Their density varies from 3.4 to 3.8. The Allende meteorite belongs to this group.
- SM, Migea type (Ukraine): the most important group. Contain from 0.6% to 2.9% carbon, 13% water. Chondrules are clearly visible, they may contain some amino acids, an example is the Marchison meteorite, which is part of this group.
- CI, Ivuna type (Tanzania): contain 3-5% carbon, 30% water and the form of hydrides of silicon and magnesium compounds. They also contain complex organic molecules and some amino acids. The Orguil meteorite belongs to this group.
After the latest discoveries, 4 more groups were added:
- SK, Karunda type (Australia): similar to the CO and CV types, but with traces of cracks from impacts received as a result of collisions in space.
- CR, Renazzo type (Italy): originally classified as CM, but reclassified to CR due to high free metal content, about 10%.
- CH, type (High-Iron): for meteorites with a high (H=high) metal content, an extremely rare type similar to CR, reclassified due to its extremely high iron content.
- SV, type Bencubbin (Australia), extremely rare type, only 8 finds were made. They contain oxygen isotopes like CR and CH meteorites, iron inclusions in the form of balls and spots irregular shape and silicates.
- Rumurutites (R): Most recently discovered, these are meteorites with very low metal content, but they may contain chondrules and they are usually brecciform.
- Kakangarites (K): extremely rare, only two are known. Very rich in iron oxide.
Differentiated meteorites or achondrites
They were named in 1895. Brezina from Vienna. They represent about 7% of all known meteorites, are very poor in iron, and are usually stony meteorites without chondrules.
Their structure and mineral composition suggest that they were formed in magma similar to that which gave rise to the earth's rocks of igneous origin: this idea is now confirmed by meteorites with a granular structure or with oriented crystals of plagioclase or pyroxene.
They are divided into the following:
- Howardites, Eucrites, Diogenites (HED): these are fragments of the surface of differentiated asteroids such as Vesta. They are very similar to basalts, gabbros and other rocks of volcanic origin, their age is 4.1-4.6 billion years.
- Ureilites (URE): It is now clear that they could be called primitive achondrites. They are rich in carbon, often found in the form of nano-diamonds, making these meteorites extremely hard to cut.
- Aubrites (AUB): they were formed in neutral conditions where oxidation is impossible, contain minerals unknown on Earth.
- Angrites (ANG): One of the rarest types, their origin is still debated, but they may have come from the surface of an asteroid.
- Shergottites, Naklitites, Chassignites (CNC): three meteorites that give their name to a group of about fifty meteorites from Mars. Their ages vary, but they are similar to terrestrial basalt rocks. They are only achondrites and contain water.
- Lunar Basalts and Breccias (LUN): This is a group of over fifty meteorites. Comparing them with samples brought to Earth by astronauts from the Apollo expeditions made it possible to verify their lunar origin.
Four new groups of primitive achondrites have been added more recently:
- Braccinites (BRA): Only eight are known. Contain a lot of free metal.
- Lodranites (LOD): these meteorites for a long time were considered mesosiderites, but have recently been reclassified as primitive achondrites.
- Acapulcoitis (ACA) and
- Vinonaites (WIN): very rich in free metal.
Iron meteorites are the most large group finds of meteorites outside the hot deserts of Africa and the ice of Antarctica, since non-specialists can easily identify them by their metallic composition and large weight. In addition, they weather more slowly than stony meteorites and, as a rule, have significantly big sizes by virtue of high density and strength, preventing their destruction when passing through the atmosphere and falling to the ground. Despite this fact, as well as the fact that iron meteorites with a total mass of more than 300 tons account for more than 80% of the total mass of all known meteorites, they are relatively rare. Iron meteorites are often found and identified, but they account for only 5.7% of all observed impacts. In terms of classification, iron meteorites are divided into groups according to two completely different principles. The first principle is a kind of relic of classical meteoritics and involves the division of iron meteorites by structure and dominant mineral composition, and the second is a modern attempt to divide meteorites into chemical classes and correlate them with certain parent bodies. Structural classification Iron meteorites are mainly composed of two iron-nickel minerals - kamasite with a nickel content of up to 7.5% and taenite with a nickel content of 27% to 65%. Iron meteorites have a specific structure, depending on the content and distribution of one or another mineral, on the basis of which classical meteorology divides them into three structural classes. OctahedritesHexahedritesAtaxitesOctahedrites
Octahedrites consist of two metal phases - kamacite (93.1% iron, 6.7% nickel, 0.2 cobalt) and taenite (75.3% iron, 24.4% nickel, 0.3 cobalt) which form a three-dimensional octahedral structures. If such a meteorite is polished and its surface treated with nitric acid, the so-called Widmanstätt structure appears on the surface, a delightful play geometric shapes. These groups of meteorites vary depending on the width of the kamasite bands: coarse-grained nickel-poor broadband octahedrites with band widths greater than 1.3 mm, medium-textured octahedrites with band widths from 0.5 to 1.3 mm, and fine-grained nickel-rich octahedrites with band widths less than 0.5 mm. Hexahedrites Hexahedrites consist almost entirely of nickel-poor kamasite and do not reveal a Widmanstätten structure when polished and etched. In many hexahedrites, after etching, thin parallel lines appear, the so-called Neumann lines, reflecting the structure of kamasite and, possibly, resulting from impact, a collision of the parent body of the hexahedrite with another meteorite. Ataxites After etching, ataxites show no structure, but, unlike hexahedrites, they are composed almost entirely of taenite and contain only microscopic kamasite lamellae. They are among the richest in nickel (the content of which exceeds 16%), but also the rarest meteorites. However, the world of meteorites is amazing world: paradoxically, the most big meteorite on Earth, the Goba meteorite from Namibia, weighing more than 60 tons, belongs to a rare class of ataxites.
Chemical classification In addition to the iron and nickel content, meteorites vary in the content of other minerals, as well as in the presence of traces of rare earth metals such as germanium, gallium, and iridium. Studies of the ratio of trace metals to nickel have shown the presence of certain chemical groups of iron meteorites, each of which is believed to correspond to a specific parent body. Here we will briefly touch on the thirteen identified chemical groups, it should be noted that about 15% of known iron meteorites do not fall into them meteorites that chemical composition unique. Compared to the iron-nickel core of the Earth, most iron meteorites represent the cores of differentiated asteroids or planetoids that must have been destroyed by catastrophic impact before falling to Earth as meteorites! Chemical groups:IABICIIABIICIIDIIEIIFIIIABIIICDIIIEIIIFIVAIVBUNGRIAB Group A significant part of iron meteorites belongs to this group, in which all structural classes are represented. Particularly common among meteorites of this group are large and medium-sized octahedrites, as well as iron meteorites rich in silicates, i.e. containing more or less large inclusions of various silicates, chemically closely related to uinonaites, a rare group of primitive achondrites. Therefore, both groups are considered to originate from the same parent body. Often IAB group meteorites contain inclusions of bronze-colored iron sulfide troilite and black graphite grains. Not only does the presence of these vestigial forms of carbon indicate a close relationship of the IAB group with the Carboniferous chondrites; This conclusion can also be made by the distribution of microelements. IC Group The much rarer iron meteorites of the IC group are very similar to the IAB group, with the difference that they contain less rare earth trace elements. Structurally, they belong to coarse-grained octahedrites, although IC group iron meteorites with a different structure are also known. Typical for this group is the frequent presence of dark inclusions of cementite cohenite in the absence of silicate inclusions. Group IIAB Meteorites of this group are hexahedrites, i.e. consist of very large individual kamasite crystals. The distribution of trace elements in Group IIAB iron meteorites resembles their distribution in some Carboniferous chondrites and enstatite chondrites, suggesting that Group IIAB iron meteorites originate from a single parent body. Group IIC Group IIC iron meteorites include the finest-grained octahedrites with kamasite bands less than 0.2 mm wide. The so-called “filling” plessite, a product of a particularly fine synthesis of taenite and kamasite, also found in other octahedrites in a transitional form between taenite and kamasite, is the basis of the mineral composition of iron meteorites of group IIC. Group IID Meteorites of this group occupy a middle position on the transition to fine-grained octahedrites, characterized by a similar distribution of trace elements and a very high content of gallium and germanium. Most Group IID meteorites contain numerous inclusions of the iron-nickel phosphate schreibersite, an extremely hard mineral that often makes Group IID iron meteorites difficult to cut. Group IIE Structurally, Group IIE iron meteorites belong to the class of medium-grained octahedrites and often contain numerous inclusions of various iron-rich silicates. Moreover, unlike meteorites of group IAB, silicate inclusions do not have the form of differentiated fragments, but of solidified, often clearly defined drops, which give iron meteorites of group IIE optical attractiveness. Chemically, group IIE meteorites are closely related to H-chondrites; it is possible that both groups of meteorites originate from the same parent body. Group IIF This small group includes plessite octahedrites and ataxites, which have high content nickel, as well as a very high content of trace elements such as germanium and gallium. There is a certain chemical similarity with both the pallasites of the Eagle group and the Carboniferous chondrites of the CO and CV groups. It is possible that the pallasites of the Eagle group originate from the same parent body. Group IIIAB After group IAB, the most numerous group of iron meteorites is group IIIAB. Structurally, they belong to coarse and medium-grained octahedrites. Sometimes inclusions of troilite and graphite are found in these meteorites, while silicate inclusions are extremely rare. However, there are similarities with the main group pallasites, and both groups are now believed to be descended from the same parent body.
Group IIICD Structurally, group IIICD meteorites are the finest-grained octahedrites and ataxites, and in chemical composition they are closely related to group IAB meteorites. Like the latter, Group IIICD iron meteorites often contain silicate inclusions, and both groups are now thought to originate from the same parent body. As a result, they also have similarities with winonaites, rare group primitive achondrites. Typical of group IIICD iron meteorites is the presence of the rare mineral hexonite (Fe,Ni) 23 C 6, which is present exclusively in meteorites. Group IIIE Structurally and chemically, group IIIE iron meteorites are very similar to group IIIAB meteorites, differing from them in the unique distribution of trace elements and typical hexonite inclusions, which makes them similar to group IIICD meteorites. Therefore, it is not entirely clear whether they form an independent group descending from a separate parent body. Perhaps further research will answer this question. Group IIIF Structurally, this small group includes coarse to fine-grained octahedrites, but is distinguished from other iron meteorites by both its relatively low nickel content and the very low abundance and unique distribution of certain trace elements. Group IVA Structurally, group IVA meteorites belong to the class of fine-grained octahedrites and are distinguished by a unique distribution of trace elements. They have inclusions of troilite and graphite, while silicate inclusions are extremely rare. The only notable exception is the anomalous Steinbach meteorite, a historical German find, as it is almost half red-brown pyroxene in a type IVA iron-nickel matrix. Whether it is a product of an impact on an IVA parent body or a relative of pallasites and therefore a stony-iron meteorite is currently being vigorously debated. Group IVB
All iron meteorites of group IVB have a high nickel content (about 17%) and structurally belong to the class of ataxites. However, when observed under a microscope, one can notice that they do not consist of pure taenite, but rather have a plessite nature, i.e. formed due to the fine synthesis of kamacite and taenite. A typical example of group IVB meteorites is Goba from Namibia, the largest meteorite on Earth. UNGR Group This abbreviation, meaning “out-of-group,” refers to all meteorites that cannot be classified into the above-mentioned chemical groups. Although researchers currently classify these meteorites into twenty different small groups, for a new meteorite group to be recognized, it generally requires at least five meteorites to be included, as established by the requirements of the Meteorite Society's International Nomenclature Committee. The presence of this requirement prevents the hasty recognition of new groups, which later turn out to be only an offshoot of another group.
