What types of meteorites are distinguished by their chemical composition. Meteors, meteorites

Updated 10.24.2018

There are three main types of meteorites (type of meteorites) depending on the dominant composition of meteorite matter:

stone meteorites - the composition of the meteorite is dominated by mineral material

iron meteorites - the meteorite is dominated by the metal component

iron-stone meteorites - the meteorite is composed of mixed material

This is a traditional, classical classification of meteorites, quite simple and convenient. However, the modern scientific classification of meteorites is based on the division into groups in which meteorites have common physical, chemical, isotopic and mineralogical properties ...

Stone meteorites

Stone meteorites ( stony meteorites - English) at first glance resemble earth stones. It is the most common type of meteorite (about 93% of all falls). There are two groups of stone meteorites: chondrites (overwhelming 86%) and achondrites.

olivines (Fe, Mg) 2 - (fayalite Fe2 and forsterite Mg2)

pyroxenes (Fe, Mg) 2Si2O6 - (ferrosilite Fe2Si2O6 and enstatite Mg2Si2O6)

Chondrules are absent in achondrites. It has been established that achondrites are fragments of planets and asteroids, for example, meteorites from Mars and the Moon are achondrites. The structure and composition of these stony meteorites are similar to those of terrestrial basalts. Achondrites are a fairly common type of meteorite (about 8% of all found meteorites).

Stone meteorites contain inclusions of nickel iron (usually no more than 20% of the mass), as well as another meteorite metal. According to experts, the age of stone meteorites is about 4.5 billion years.

Iron meteorites

Iron meteorites ( iron meteorites - English) consist mainly of metal, a mixture (alloy) of iron and nickel in various proportions, and they also contain inclusions of other elements and minerals, but they rarely account for more than 20% of the mass (about 6% of falls). The Ni content in iron meteorites ranges from 5 to 30% or more.

Even an ordinary ground metal detector responds to this type of meteorite most clearly. The fracture of the meteorite has a characteristic metallic luster. The melting crust is gray or brown in color, so it is difficult to visually distinguish an iron meteorite from an ordinary stone.

Iron stone meteorites

Iron-stone meteorites ( iron-stony meteorites - English) is a fairly rare type of meteorite (about 1.5% of falls). The composition of these meteorites is intermediate between stone and iron meteorites. There are two groups of iron-stone meteorites: pallasites and mesosiderites.

The structure of pallasite is translucent crystals of olivine (Fe, Mg) 2, enclosed in a matrix of iron and nickel. Pallasites at the fracture (in section) have an attractive aesthetic appearance and are a welcome purchase for collectors. The cost of these meteorites is in the range of $ 6 - $ 60 or more per gram of meteorite matter.

Mesosiderites it is a very rare type of meteorite (about 0.5% of falls). The composition of mesosiderites includes iron, nickel, and silicate minerals such as pyroxenes, olivine, and feldspar in approximately equal proportions.

The most valuable, both from the point of view of science and from the point of view of business on meteorites and collecting, are primarily meteorites from Mars and the Moon, as well as the entire "family" of iron-stone meteorites.

Related tags: types of meteorites, types of meteorites, classification of meteorites, stone meteorites, iron - stone meteorites, iron meteorites, chondrites, achondrites, pallasites, mesosiderites, what kind of meteorites are, chemical composition of meteorites, meteorite in section, meteorite at a break

A meteorite is a body of cosmic origin that fell on the surface of a large celestial object. Most of the meteorites found have a mass of a few grams to several kilograms (the largest of the found meteorites is Goba, whose mass was estimated to be about 60 tons). It is believed that 5-6 tons of meteorites fall to the Earth per day, or 2 thousand tons per year.

A space body up to several meters in size, flying in orbit and entering the Earth's atmosphere, is called a meteoroid, or meteoroid. Larger bodies are called asteroids. The phenomena generated by the passage of meteoric bodies through the Earth's atmosphere are called meteors or, in general, a meteor shower, especially bright meteors are called fireballs. A solid body of cosmic origin that has fallen to the surface of the Earth is called a meteorite. Other names for meteorites: aeroliths, siderolites, uranolites, meteorolites, batylyams, celestial, air, atmospheric or meteoric stones, etc.

A crater (astroblema) may form at the site of a large meteorite. One of the most famous craters in the world is Arizona. The largest meteorite crater on Earth is believed to be Wilkes Land Crater (about 500 km in diameter).

External signs of a meteorite

The main outward signs of a meteorite are melting crust, regmaglipts, and magnetism. In addition, meteorites are generally irregular in shape (although round or cone-shaped meteorites are also found).

Melting crust

A melting crust forms on a meteorite as it travels through the earth's atmosphere, which can cause it to heat up to temperatures around 1800 °. It is a melted and re-solidified thin layer of meteorite matter. As a rule, the melting crust is black and dull; inside the meteorite is lighter in color.

Regmaglipts

Regmaglipts are characteristic depressions on the surface of a meteorite, reminiscent of fingerprints on soft clay. They also occur when a meteorite moves through the earth's atmosphere as a result of ablation processes.

Magnetic properties

Meteorites have magnetic properties, and not only iron, but also stone. This is explained by the fact that most stone meteorites contain inclusions of nickel iron.

Composition of meteorites

Meteorites are divided into three groups in composition:

1. Stone
   1. chondrites (carbonaceous chondrites, common chondrites, enstatite chondrites)
2. Iron (or the old name - siderites)
3. Iron-stone
   1. pallasites
   2. mesosiderites

Stone meteorites

The most common are stone meteorites (92.8% of falls). They consist mainly of silicates: olivines and pyroxenes.

Chondrites

The vast majority of stone meteorites (92.3% stone, 85.7% of the total number of falls) are chondrites. They are called chondrites because they contain chondrules - spherical or elliptical formations of predominantly silicate composition. Most chondrules are no more than 1 mm in diameter, but some can reach several millimeters. Chondrules are found in a detrital or fine-crystalline matrix, and often the matrix differs from chondrules not so much in composition as in crystal structure. The composition of chondrites is almost identical to the chemical composition of the Sun, with the exception of light gases such as hydrogen and helium. Therefore, it is believed that chondrites were formed directly from the protoplanetary cloud surrounding the Sun by condensation of matter and dust accretion with intermediate heating.

Achondrites are a very heterogeneous class of meteorites. They differ significantly from the common chondrites, primarily by the absence of chondrules. They are similar in composition and structure to terrestrial basalts. All achondrites to one degree or another underwent melting, which destroyed the chondrules. Achondrites are a fairly common type of meteorite. They make up about 8% of all found meteorites. Achondrites make up 7.3% of stony meteorites. These are fragments of protoplanetary and planetary bodies that have undergone melting and differentiation in composition (into metals and silicates). In the course of evolution, they were exposed to high temperatures, which means that at some point they dissolved in magma. When magma cools and crystallizes, it creates concentric layered structures. Generally speaking, achondrite is a stony meteorite that forms from the molten material of its original object of origin; they resemble basalts formed by magmatic processes in the bowels of the Earth. Thus, achondrites have a differentiated structure, having lost a significant part of their original materials, including metals, and, as a rule, do not contain chondrules.

Iron meteorites

The largest known meteorites are iron. Iron meteorites are composed of an iron-nickel alloy. They account for 5.7% of the falls. The largest of them all is located at the crash site in Goba, Namibia, weighing 59 tons. Iron meteorites rarely change shape when entering the atmosphere and suffer much less from the effects of ablation when passing through dense layers of air. All iron meteorites ever found on Earth weigh more than 500 tons, and they make up approximately 89.3% of the mass of all known meteorites. Despite these facts, iron meteorites are rare. Iron meteorites are composed primarily of iron and nickel. Most of them include only minor admixtures of minerals. There is a wide variety among iron meteorites and it has always been difficult to classify them. In fact, they are divided into 13 groups according to their chemical composition, with special attention paid to the amount of gallium, germanium and iridium contained in meteorites in hundredths of a percent. Most of the known achondrites are of the so-called HED type, and according to many geochemists, they originate from the asteroid West. Other achondrites come from Mars, the Moon, and other asteroids not yet identified.

Iron silicate meteorites

Iron-silicate meteorites have an intermediate composition between stony and iron meteorites. They are relatively rare (1.5% falls).

Pallasite (from the Pallas iron meteorite) is a class in the type of iron-stone meteorites. This rare type of iron-stone meteorites is an iron-nickel base interspersed with olivine crystals (sometimes up to 15 mm). Named after academician P.S. Pallas, who described it as native iron. The nickel content in the metal is about 10%. Pallasite is composed of approximately equal amounts of nickel iron and olivine. The peculiar structure of Pallasite indicates that they were formed in the absence of at least significant gravitational forces. Pallasites are undoubtedly the most beautiful meteorites, especially when sawn and polished!

Mesosiderites are iron-stone meteorites, consisting of approximately equal parts of iron, nickel, and silicate minerals (olivine, pyroxenes, and calcium feldspars). Mesosiderites have a heterogeneous brecciated structure. Silicate minerals and metals are often present in them in the form of rounded and acute-angled fragments and fine-grained intergrowths. The composition of Mesosiderites (on average): 45% nickel iron (in the form of inclusions in the stony mass), 30% hypersthene, 16.4% anorthite and a small amount of some other minerals. Mesosiderites are very rare meteorites. As of June 2009, only 145 mesosiderites were known (44 of them in Antarctica). In 7 cases out of 145 discovered mesosiderites, their falls were observed. Some fragments of mesosiderites are among the largest known meteorites (up to several tons).

Meteorite, meteor, meteoroid

Updated 10.24.2018

There are three main types of meteorites (type of meteorites) depending on the dominant composition of meteorite matter:

stone meteorites - the composition of the meteorite is dominated by mineral material

iron meteorites - the meteorite is dominated by the metal component

iron-stone meteorites - the meteorite is composed of mixed material

This is a traditional, classical classification of meteorites, quite simple and convenient. However, the modern scientific classification of meteorites is based on the division into groups in which meteorites have common physical, chemical, isotopic and mineralogical properties ...

Stone meteorites

Stone meteorites ( stony meteorites - English) at first glance resemble earth stones. It is the most common type of meteorite (about 93% of all falls). There are two groups of stone meteorites: chondrites (overwhelming 86%) and achondrites.

olivines (Fe, Mg) 2 - (fayalite Fe2 and forsterite Mg2)

pyroxenes (Fe, Mg) 2Si2O6 - (ferrosilite Fe2Si2O6 and enstatite Mg2Si2O6)

Chondrules are absent in achondrites. It has been established that achondrites are fragments of planets and asteroids, for example, meteorites from Mars and the Moon are achondrites. The structure and composition of these stony meteorites are similar to those of terrestrial basalts. Achondrites are a fairly common type of meteorite (about 8% of all found meteorites).

Stone meteorites contain inclusions of nickel iron (usually no more than 20% of the mass), as well as other. According to experts, the age of stone meteorites is about 4.5 billion years.

Iron meteorites

Iron meteorites ( iron meteorites - English) consist mainly of metal, a mixture (alloy) of iron and nickel in various proportions, and they also contain inclusions of other elements and minerals, but they rarely account for more than 20% of the mass (about 6% of falls). The Ni content in iron meteorites ranges from 5 to 30% or more.

Even an ordinary meteorite reacts most clearly to this type of meteorite. The fracture of the meteorite has a characteristic metallic luster. The melting crust is gray or brown in color, so it is visually difficult.

Iron stone meteorites

Iron-stone meteorites ( iron-stony meteorites - English) is a fairly rare type of meteorite (about 1.5% of falls). The composition of these meteorites is intermediate between stone and iron meteorites. There are two groups of iron-stone meteorites: pallasites and mesosiderites.

The structure of pallasite is translucent crystals of olivine (Fe, Mg) 2, enclosed in a matrix of iron and nickel. Pallasites at the break (in section) have an attractive aesthetic appearance and are a desirable acquisition for collectors. is in the range of $ 6 - $ 60 or more per gram of meteorite matter.

Mesosiderites it is a very rare type of meteorite (about 0.5% of falls). The composition of mesosiderites includes iron, nickel, and silicate minerals such as pyroxenes, olivine, and feldspar in approximately equal proportions.

The most valuable, both from the point of view of science and from the point of view of business on meteorites and collecting, are, first of all, and also the entire "family" of iron-stone meteorites.

Related tags: types of meteorites, types of meteorites, classification of meteorites, stone meteorites, iron - stone meteorites, iron meteorites, chondrites, achondrites, pallasites, mesosiderites, what kind of meteorites are, chemical composition of meteorites, meteorite in section, meteorite at a break

Quite often, an ordinary person imagining what a meteorite looks like, thinks about iron. And this is easy to explain. Iron meteorites are dense, very heavy, and often take on unusual and even dramatic shapes as they fall and melt in our planet's atmosphere. Although iron is associated by most people with the typical composition of space rocks, iron meteorites are one of the three main types of meteorites. And they are quite rare in comparison with stone meteorites, especially with the most common group of them - single chondrites.

Three main types of meteorites

There are many types of meteorites, divided into three main groups: iron, stone, stone-iron. Nearly all meteorites contain extraterrestrial nickel and iron. Those of them that do not contain iron at all are so rare that even if we ask for help in identifying possible space stones, we most likely will not find anything that does not contain a large amount of metal. The classification of meteorites is, in fact, based on the amount of iron in the sample.

Iron meteorites

Iron meteorites were part of the core of a long-lost planet or a large asteroid from which it is believed to have formed Asteroid Belt between Mars and Jupiter. They are the densest materials on Earth and are very attracted to a strong magnet. Iron meteorites are much heavier than most of the earth's rocks, if you've lifted a cannonball or a slab of iron or steel, you know what this is about.

Most of the samples in this group have an iron content of about 90% -95%, the rest is nickel and trace elements. Iron meteorites are classified into classes according to their chemical composition and structure. Structural classes are determined by studying two components of iron-nickel alloys: kamacite and tenite.

These alloys have a complex crystalline structure known as the Widmanstätten structure, named after Count Alois von Widmanstetten, who described the phenomenon in the 19th century. This lattice-like structure is very beautiful and is clearly visible if an iron meteorite is cut into plates, polished and then etched in a weak solution of nitric acid. In the kamacite crystals found in the process, the average width of the bands is measured, the resulting figure is used to classify iron meteorites into structural classes. Iron with a thin strip (less than 1 mm) is called "fine-structured octahedrite", with a wide strip "coarse octahedrite".

Stone meteorites

The largest group of meteorites - stone, they formed from the outer crust of a planet or an asteroid. Many stone meteorites, especially those that have been on the surface of our planet for a long time, are very similar to ordinary earth stones, and it takes an experienced eye to find such a meteorite in the field. Recently fallen stones feature a black, shiny surface that was formed by surface burning in flight, and the vast majority of stones contain enough iron to be attracted to a powerful magnet.

Some stony meteorites contain small, colorful, grain-like inclusions known as chondrules. These tiny grains originated from the solar nebula, therefore, even before the formation of our planet and the entire solar system, which makes them the oldest known matter available for study. The stony meteorites containing these chondrules are called chondrites.

Cosmic stones without chondrules are called achondrites. These are volcanic rocks formed by volcanic activity on their "parent" space objects, where melting and recrystallization has erased all traces of ancient chondrules. Achondrites contain little or no iron, making it difficult to find when compared to other meteorites, although specimens are often covered with a glossy crust that looks like enamel paint.

Stone meteorites from the Moon and Mars

Can we really find lunar and Martian rocks on the surface of our own planet? The answer is yes, but they are extremely rare. More than one hundred thousand lunar and approximately thirty Martian meteorites have been discovered on Earth, and they all belong to the achondrite group.

The collision of the surface of the Moon and Mars with other meteorites threw the debris into open space and some of them fell to Earth. From a financial point of view, lunar and Martian samples are among the most expensive meteorites. In collector's markets, their prices go up to thousands of dollars per gram, which makes them several times more expensive than if they were made of gold.

Stone-iron meteorites

The least common of the three main types - stone-iron, accounts for less than 2% of all known meteorites. They consist of approximately equal parts of iron-nickel and stone, and are divided into two classes: pallasites and mesosiderites. Stone-iron meteorites formed on the border of the crust and mantle of their "parent" bodies.

Pallasites are perhaps the most tempting of all meteorites and are definitely of great interest to private collectors. Pallasite consists of an iron-nickel matrix filled with olivine crystals. When olivine crystals are clear enough to appear emerald green, they are known as the Perodotus gemstone. The Pallasites got their name in honor of the German zoologist Peter Pallas, who described the Russian meteorite Krasnoyarsk, found near the capital of Siberia in the 18th century. When a pallasite crystal is cut into plates and polished, it becomes translucent, giving it an unearthly beauty.

Mesosiderites are the smaller of the two stone-iron groups. They are composed of iron-nickel and silicates and are usually attractive in appearance. The high contrast of the silver and black matrix, if you cut off the plate and grind, and random inclusions, leads to a very unusual look. The word mesosiderite comes from the Greek "half" and "iron," and they are very rare. In thousands of official catalogs of meteorites, there are less than a hundred mesosiderites.

Classification of meteorites

The classification of meteorites is a complex and technical subject and the above is intended only as a brief overview of the topic. The classification methods have changed several times in recent years; known meteorites have been reclassified to a different class.

Study of meteorites.

Tunguska meteorite

4. Stone meteorites

6.

Fossils of ancient Martian life?

8. LIST OF REFERENCES:

Study of meteorites. Cosmogonic ideas

Russian scientists of the late 18th and early 19th centuries. plays a prominent role in the study of meteorites falling to Earth from world space. The question of the origin of meteorites before the end of the XVIII century. remained open. They believed that they could not fall from the sky and were of earthly origin.

In 1772, Academician Pallas brought from Siberia a huge piece of iron, weighing more than half a ton, found in 1749 by a blacksmith from the village of Medvedeva near the Yenisei River. This iron mass is still kept in the Geological Museum of the Academy of Sciences. Just in the same 1772, the famous French scientist Lavoisier, together with other academicians, signed a protocol at the Paris Academy of Sciences, which stated that "the fall of stones from the sky is physically impossible." (The word “stones” meant both iron and stone meteorites.) When a stone rain fell in France in 1790 and this was registered by the local city government, Academician Berthollet wrote: “How sad that an entire municipality is bringing in protocol folk tales, passing them off as really seen, while not only physics, but also nothing reasonable, in general, they cannot be explained. " Such views on meteorites did not contribute to their study; there were even cases that the curators of some museums, fearing to be accused of ignorance, threw meteorites from their collections.

In 1794, a book was published in Riga by a Leipzig scientist who was a corresponding member of the St. Petersburg Academy of Sciences, E.F. Khladny (1756-1827), who proved the extraterrestrial, cosmic origin of the Pallas Iron. After collecting information about the observed flights of fireballs - fireballs and the falls of meteorites, Khladny correctly put them in communication with each other. Thus, being the founder of the science of meteorites, Khladny defended their cosmic origin, but the correctness of his conclusions was recognized only much later.

In 1807 prof. Physics of Kharkov University A.I. Stoykovich published a comprehensive monograph on meteorites based on the practical material collected in it. True, Stoikovich was inclined to the opinion of the atmospheric origin of meteorites, but did not reject the possibility of their cosmic origin. In 1819, a remarkable book by chemist I. Mukhin was published in St. Petersburg, in which, in addition to describing meteorites, data were also given on their chemical composition.

Interest in the science of the universe among the advanced strata of Russian society was very great even before this science took its place in universities. This is evidenced, in particular, by the inventories of things that survived the Moscow fire of 1812, where various telescopes belonging to private individuals appear. Lovers of astronomy were not only in the capitals, but also in the provinces. For example, in the Public Library. Saltykov-Shchedrin in Leningrad, a homemade, intricate and lovingly painted, very complex mobile calendar has been preserved. This calendar with data on the planets and with Ukrainian names of months, with its own verses, was compiled in 1812 by a certain Dmitry Timofeev in the Vorobyovka settlement of the Kherson province, then still a remote Russian province.

Among astronomy lovers of the late 18th and early 19th centuries. I.D. Ertov (1777-1828). Not knowing foreign languages, he was not familiar with the cosmogonic hypotheses of Kant and Laplace. However, studying the scientific literature available to him in Russian and thinking about the origin and development of celestial bodies, Ertov made an attempt to state his own cosmogonic views, in which his materialistic worldview was clearly manifested. His indisputable merit is the support of the hypothesis that celestial bodies arose from scattered "foggy matter", which, according to chemical laws, decomposed into various simple and complex substances. He originally presented for his time the origin of planetary satellites as a result of the capture of comets by planets and explained the origin of the earth's crust. His first work, "The History of the Origin of the Universe", was presented to the Academy of Sciences in 1797. In 1805, he published the book "Thoughts on the Origin and Formation of Worlds," republished in 1811. The Otechestvennye Zapiski magazine in 1821, noting the lack of scientific knowledge Ertov, appreciated, however, the originality of his searches. This attracted public attention to Ertov's hypothesis, but his works, poorly developed theoretically, did not influence science and they were soon forgotten.

The structure and age of meteorites

Iron meteorites, as already mentioned, are easier to detect, easily rust and turn brown. Their shape is always irregular, and the surface, if it has not yet had time to oxidize, is covered with smooth black bark - scale. This thin crust results from the melting of the outer layer of the meteorite as it falls through the air. The meteorite flies, however, so fast that, with any significant mass, it does not have time to warm up inside, and its molten surface solidifies into a thin crust already at the last stage of its (slow) fall, even before falling to the ground. The temperature of a meteorite during its fall and flight is almost the same as during its movement past the Earth. This is the temperature of a body heated by the Sun at the distance of the Earth. This temperature is about 4 ° above zero. Contrary to fantastic stories, the interior of the meteorites is not red-hot and is not cooled to absolute zero (i.e., to 273 ° C).

The surface of the meteorite iron, polished and etched with a weak acid, is covered with a pattern resembling frost on the windows and due to the peculiarities of the crystal structure of this iron. This drawing is called the Widmanstätten figures, and it unmistakably helps to distinguish meteoric iron from native or smelted from ore.

Stone meteorites are usually covered with a thin black glassy crust, sometimes matte, sometimes shiny. It is weathered and oxidized if the meteorite lies in the open air or in the ground for a long time, and then it is even more difficult to distinguish the meteorite from the earth's stone. Inside, at the break, the meteorite is of different types. Most often it is gray, sometimes with round grains of a special structure (they are called chondrules) and with metallic sparkles.

The polished surface of a meteorite, viewed under a microscope, presents for a specialist a special characteristic structure that distinguishes it from the earth's stone, although not only the chemical, but also the mineralogical composition of them is very similar. Such a specialist is no longer an astronomer, but a mineralogist, or rather a petrographer 1, and, moreover, a special study of meteorites. With the assistance of academicians V.I. Vernadsky and A.E. Fersman, a whole school of such specialists in meteorites was formed in the USSR: P.L. Dravert, P.N. Chirvinsky, L.A. Kulik and others. In the jurisdiction of astronomers, the meteorite is actually only as long as it is a celestial body, that is, it is outside the Earth. An astronomer can still meet such a guest on the doorstep of his home - the Earth, that is, he can determine its trajectory in the atmosphere, but to understand the details of the structure of stones - for this you need to have another special education and extensive experience in studying stones and minerals. The science of petrography, as a result of a detailed study of meteorites, divides them in structure into many classes that differ in different features.

Figure: 106. Widmanstätten figures on the polished surface of an iron meteorite, acid-etched.

When a meteorite flies in the air, a powerful "wind" blows it from the front and from the sides and, melting the surface, blows off easily melting substances from it, and also generally smooths out sharp edges and corners. Therefore, the outline of the meteorite, if it did not split at the very end of its path, is more rounded than it had in airless space. The air seems to grind the meteorite, but the result of such processing depends on the speed of the meteorite, on its shape, on its rotation in flight. Often a meteorite is shaped like a piece of clay, crumpled with fingers. On its surface, hollows, depressions, and sometimes grooves are visible, diverging in all directions from the frontal part of the meteorite. Then the meteorite itself has a conical shape, like the head of a projectile.

We will talk about the average chemical composition of meteorites in more detail in the next section. Even before 1819 I. Mukhin was engaged in chemical analysis of meteorites in St. Petersburg. Recently, not only the qualitative, but also the quantitative chemical composition of meteorites has been established in great detail. Alas! This necessary curiosity has cost us dearly, since for the purpose of such a chemical analysis, we had to destroy, literally powdering, a large number of meteorites from the museum collections. These meteorites cannot now be subjected to any other scientific study, and meteorite researchers - not chemists cry out: “Enough of chemical analyzes, we are already satisfied with what we know about the chemistry of meteorites! Leave us something to study the size, shape and structure of meteorites! "

We have already given the average chemical composition of stony meteorites, which varies somewhat from meteorite to meteorite. Basically, they consist of oxygen (36.3% by weight), iron (25.6%), silicon (18.0%) and magnesium (14.2%). The rest of the chemical elements (all the same, but not all those that we know on Earth) are contained in the amount of one percent and fractions of a percent. In general, their composition is similar to the chemical composition of the earth's crust, especially if we consider deep rocks. Compared to them, terrestrial rocks contain more silicon and oxygen, but less iron and magnesium. The place of the latter on the Earth in minerals seems to be occupied by aluminum, but, apparently, the deeper into the Earth, the more the composition of the earth's layers resembles the composition of meteorites.

Iron meteorites, in addition to iron (91%) and nickel (8%), also contain cobalt (0.7%), phosphorus (0.2%), and in even smaller quantities - sulfur, carbon, chromium and copper.

The gold, which was already mentioned above, contains only 0.0004%, that is, if it were possible to extract gold from all the meteorites collected on Earth, then it would not have accumulated even one kilogram. However, this is almost impossible to do, since gold is dispersed in meteorites; and the sense in this would be the same as earning a livelihood by selling pins dropped by summer residents among the autumn leaves in the forest.

It is interesting that in 1946 the Soviet petrographer L.G. Kvasha under the leadership of academician A.N. Zavaritsky, in one of the meteorites, 8% of the water was found, which, however, is part of the minerals, and not free.

Even less than gold, meteorites contain radioactive elements - uranium, radium, thorium and others, moreover, radium itself - 0.00000000001%, or 20 times less than it is in rocks. However, finding this insignificant amount of radioactive elements in meteorites is incomparably more important than finding gold or diamonds in them, even if there are even a hundred times more of them than there actually are.

Radioactive elements and their companion - helium gas - replace their "metric certificate" for meteorites, giving out the age of our heavenly guests.

Uranium and thorium, spontaneously decaying, are transformed, as is known, into other chemical elements, while releasing heat, electrons, X-rays and helium atoms. At the end of this chain of atomic transformations lies lead, which no longer shows a tendency to decay further.

It is also known the "stubbornness" with which the atoms of radioactive elements decay and follow the law of this decay, ignoring attempts to accelerate or slow down their decay.

No matter how much uranium is available, in 4560 million years half of its atoms decays, i.e., for example, half of a gram of uranium in 4560 million years will remain (half a gram). Of this half, after the next 4560 million years, half will remain again, that is, g. The same is done by thorium, but more lazily, decaying by half in 13,000 million years, and radium (an intermediate product of the decay of uranium), on the contrary, is much more energetic : half of it will remain after 1600 years.

Light atoms of helium, ejected from the depths of heavy atoms of radioactive elements, accumulate in the solid mass containing them. It is not difficult to determine how much helium should accumulate as a result of the decay of, say, 1 g of uranium. But in this case, it is easy to calculate how long it takes for uranium to decay in a given stone, if by now there are so many grams of it in the stone, and so many grams of helium. Obviously, thorium and uranium decay in each stone for as long as they are in it, that is, from the time the stone was formed, say, after it solidified from a molten mass, from which helium could not escape and from which the uranium also could not escape in any way. After the solidification of the stony mass, uranium and its decay products were imprisoned in it for life, as in a prison.

Thus, the ratio of helium and uranium found in a stone determines the age of the stone and, moreover, with a relative accuracy, perhaps greater than that with which we can estimate his age by the appearance of a person.

This method determined the age of various terrestrial rocks and found that the most ancient of them in the earth's crust are 3-3½ billion years old. The same is the age of the hard earth's crust, a very respectable age.

Paneth and his collaborators have done an extremely difficult determination of the content of uranium and helium in many meteorites - difficult because there are very few of them. The results obtained for several dozen meteorites led to an unexpected conclusion.

It turned out that the "ages" of meteorites are in the range from 60 to 7600 million years! It seemed that scientists managed to get their hands on very "young" celestial bodies, since 60 million years for a celestial body is downright infancy.

But it soon became clear that the surprising spread in the ages of meteorites is explained not by the real difference in the time of their "life", but simply by the difference in the "conditions of existence." The fact is that the ratio of helium and lead in a meteorite depends not only on its age, but also on the intensity of irradiation of meteorites by cosmic rays - a stream of particles of enormous energy. It was not so easy to separate helium of "cosmic" and "internal" origin. When this succeeded, the ages of the meteorites turned out to be much more similar: from 2½ to 4 billion years.

By the way, we have not yet said anything about the mineralogical and petrographic structure of the aliens from the sky.

Indeed, the same atoms can form different molecules, connecting in different combinations, and all the more complex compounds called minerals can be built from them.

The main minerals that make up stone meteorites are known and widespread on Earth. I hope not to tire you by listing, for example, olivine, pyroxene, feldspar, plagioclase, nickel iron. However, many terrestrial minerals are absent in meteorites, for example, orthoclase and mica, although they are so common on Earth.

But meteorites introduce us to minerals that for some reason do not form on Earth, which were named after the scientists who discovered them. These are schreibersite, dobeelite, moissanite, etc.

The results of the study of the chemical and mineralogical composition of meteorites confirm a very important philosophical conclusion about the material unity of the Universe. Outside the Earth, we find, for example, the same chemical elements that the great Mendeleev placed in his table, and those that were added to it later. The laws of chemistry turn out to be valid not only on the planet where they were established. And at the same time, nature does not have that tiresome monotony to which metaphysically thinking people tried to reduce it. Mineralogical diversity in meteorites, the presence in them of minerals that are not found on the surface of the Earth, is one of the striking examples of the diversity of nature, due to the infinite qualitative variety of movements, processes occurring

Tunguska meteorite

Unfortunately, in this case, there was no extraordinary phenomenon of scientifically trained observers. Unfortunately ... and, by the way, maybe fortunately for these alleged observers. One Evenk shepherd, who witnessed the fall of the meteorite, was thrown high into the air by an air wave, and then hit the ground, as in a bomb explosion. They said about him that the poor man lost his tongue from the blow and fright, and when L.A. Kulik - the researcher of the Tunguska meteorite - found this man, then this most valuable witness of the extraordinary incident could not give his testimony. The meteorite itself fell on June 30, 1908 in the deep swampy taiga, near the Podkamennaya Tunguska River, hundreds of kilometers from the railway. It did not attract the attention of the tsarist government, and scientific study of the circumstances of this fall began only after the October Revolution.

In a number of settlements in Central Siberia, a bright fireball was observed in clear weather. At about 7 o'clock in the morning, somewhere over the Minusinsk region, it penetrated into the upper layers of the earth's atmosphere and swept through it, approaching the surface of the Earth in the northeast direction. In full sunlight, he attracted the attention of the train passengers, who were looking out the windows of the carriages that rolled along the tracks of the shortly before completed Great Siberian Railway.

Residents of Kirensk on the Lena, located at a distance of 450 km from the place of the fall, saw a fountain of explosion products that arose behind the distant taiga like a huge vertical column of smoke. In order to be seen from Kirensk, he had to rise at least 20 km in height.

The explosion wave always turns into sound; so it was in this case. In the aforementioned villages, the blast wave in houses shook glass and dishes in cupboards, and a faint sound was heard even at a distance of 700 km. Further away, the residents did not pay attention to him, but he was noted by instruments recording air pressure. These devices - barographs - marked the air wave in St. Petersburg, Copenhagen, Germany and even Washington (USA). By recording these devices, one can establish the moment when this air wave reached them, and so it was possible to trace how it went from Podkamennaya Tunguska to the east and west, gradually going further and further. Circling earth and weakening, it nevertheless continued on its way, and after 30 hours it was registered again in Potsdam (Germany).

What happened, however, at the site of the fall?

Small mountains and dense forest around the site of the fall weakened the effect of the blast wave, but nevertheless the plague of the Evenks and shepherd's huts were thrown from the place as from a storm, and their inhabitants were knocked down and received bruises. Meanwhile, these plagues were 30 km from the place of their fall.

For three years (1927-1930) L.A. Kulik discovered that the peat covering the swampy soil there was collected in folds several meters high by air pressure, torn in places into pieces and carried from place to place. In the clay were found the smallest fragments of shattered rocks that got there during the explosion. A destroyed Tungus warehouse was found nearby. In addition, more than 10 craters with a diameter of 10 to 50 m and fused pieces of quartz with traces of nickel iron were found, but not a single meteorite was found.

Figure: 109. Forest burnt and felled during the fall of the Tunguska meteorite.

The fact is that the Tunguska meteorite fell in the permafrost region, where the frozen soil at some depth never thaws. The permafrost layer does not allow water to pass through, and the subsoil water freezes at a shallow depth, raising the upper layers of the soil with mounds. From the failures of such peat mounds, craters were formed.

As shown by the calculations of K.P. Stanyukovich and V.V. Fedynsky, the most massive meteorites, such as the Tunguska and Arizona, reach the surface of the Earth without losing their cosmic speed. So, even at a speed of 4-5 km / s, a solid at the moment of impact turns out to be similar to a highly compressed gas. An instantaneous destruction of the crystal lattice of the meteorite occurs, it evaporates, turning into a gas, which then tends to expand.

Thus, a real explosion is obtained, as a result of which the meteorite produces huge destruction, but at the same time it perishes itself, turning into gas and dissipating in the air. The fragments falling out in this case can only be satellites of the meteorite, which broke away from it before falling and, due to their small mass, moved in the atmosphere much more slowly.

In 1957, microscopic particles of meteorite iron were finally discovered in the soil in the area of \u200b\u200bthe fall, although they are found in other places on Earth.

V.G. Fesenkov believed that there was a fall of not just a meteorite, but a fall of the nucleus of a small comet, but this does not change the essence of the matter. The meteorite (or rocky-ice comet nucleus) exploded due to natural causes, and therefore its remains cannot be found.

In general, it has now been established that impact craters are formed when meteorites fall at a low speed, and when a meteorite falls at a high speed and explodes, explosive craters are formed, when a meteorite can even spray completely.

4. Stone meteorites - This is the main type of meteorites falling to the Earth, and this is more than 90% of all meteorites. Stony meteorites are composed mainly of silicate minerals. There are two main types of rock meteorites - chondrites and achondrites. Both chondrites and achondrites are divided into many subgroups depending on their mineral composition and structure.

The most common type of stone meteorite is ordinary chondrite

A chondrite-type rock meteorite is the material from which the solar system was formed, and has changed little compared to the rock formations of the large planets, which have been exposed for billions of years of geological activity. They can tell us a lot about how the solar system was formed. When chondrites are studied in a thin section, then analyzing the relationship between different types of minerals, one can obtain information about the composition of the dust from which the solar system was formed, and those physical conditions (pressure, temperature) of the protoplanetary disk that were at the time of the formation of the system.

Common chondrite

Chondrites are among the most primitive rocks in the solar system. Over the past 4.5 billion years since its formation, this type of rock meteorite has not changed in composition from the composition of the asteroid from which they originated. Because they have never been exposed to the high temperature and pressure of the planet's interior. This means that they have a very characteristic appearance of droplets of silicate minerals mixed together with fine grains of sulphides and metals of iron and nickel. These structures of millimeter size (from 0.1 to 10 mm) are called "chondrules". This word "chondres" is of Greek origin and is translated as "grains of sand".

Ordinary chondrites, depending on the content of iron and silicates, are divided into 3 groups:

· H chondrites - achondrites of this group contain the most iron chondrites (25-30%) and very little iron oxide (oxidized iron);

· L chondrites - the iron content in this type of chondrites reaches 19-24%, but more iron oxide;

· LL chondrites - up to 7% pure iron, but there are many silicates in the composition.

The surface of a stone meteorite (photo meteorite.narod.ru)

Basic chondrites known as carbon chondrites (have a high concentration of carbon - up to 5% by mass), rich in water, sulfur and organic material. The rock meteorites of this group are believed to have brought organic and volatile matter to the Earth when it was formed, helping to create an atmosphere and conditions for life.

Carbonaceous chondrites

Carbonaceous chondrites (denoted by the letter "C", from the English carbonaceous - carbonaceous) are the darkest, which justifies their name. They contain a lot of iron, but it is almost entirely bound in silicates. The dark color of carbonaceous chondrites is mainly due to the mineral magnetite (Fe 3 O 4), as well as small amounts of graphite, soot, and organic compounds. These meteorites also contain a significant proportion of water-bearing minerals or hydrosilicates (serpentine, chlorite, montmorillonite, and a number of others).

J. Wasson proposed in the 1970s to divide carbonaceous chondrites into four groups (CI, CM, CO, and CV) based on the gradual change in their properties. Each group contains a typical, reference meteorite, the first letter of the name of which is added to the "C" index when the group is designated. Typical representatives in the above groups are meteorites Ivuna, Migei (found in Ukraine, in Nikolaev oblast), Ornans, and Vigarano. Somewhat earlier, in 1956, G. Wiik proposed the division of carbonaceous chondrites into three groups (CI, CII and CIII), which can sometimes be found in the literature. The Wasson groups CI and CM fully correspond to the CI and CII groups of Wiik, and the CO and CV groups can be considered as components of the CIII group.

In CI chondrites, hydrated silicates occupy most of the volume. Their X-ray studies showed that the predominant silicate is septechlorite (the general formula of septechlorites is Y 6 (Z 4 O 10) (OH) 8, where Y \u003d Fe 2+, Mg; Z \u003d Si, Al, Fe 3+). Moreover, all hydrosilicates are in amorphous form, that is, in the form of glass. There are no dehydrated silicates (pyroxenes, olivines, etc., which appear at temperatures above 100 ° C) at all. CI meteorites are an exception among chondrites, since their substance does not contain chondrules at all, but consists, as it were, of one matrix. This confirms the idea of \u200b\u200bcrystallization of chondrules from molten material, since studies show that the material of CI chondrites did not undergo melting. It is considered the most unchanged, in fact, the primary matter of the solar system, preserved from the moment of condensation of the protoplanetary cloud. This explains the high interest of scientists in CI meteorites.

CM chondrites contain only 10-15% of bound water (in the composition of hydrosilicates), while chondrules contain 10-30% of pyroxene and olivine.

CO and CV chondrites contain only 1% of water in a bound state and are dominated by pyroxenes, olivines, and other dehydrated silicates. They also contain small amounts of nickel iron. The presence of hydrosilicates markedly reduces the density of carbonaceous chondrites: from 3.2 g / cm 3 in CV to 2.2 g / cm 3 in CI meteorites.

Enstatite chondrites

In enstatite (E) chondrites, iron is found mainly in the metallic phase, that is, in a free state (at zero valence). At the same time, their silicate compounds contain very little iron. Almost all pyroxene in them is presented in the form of enstatite (hence the name of this class). The structural and mineralogical features of enstatite chondrites show that they underwent thermal metamorphism at maximum (for chondrites) temperatures, approximately in the range from 600 ° C to 1000 ° C. As a result, E-chondrites are the most reduced and contain the least volatile compounds.

In this group, there are 3 petrological types (E4, E5, and E6), in which an increase in signs of thermal metamorphism can be traced. It was also found that in the E-chondrites there are wide variations in the content of iron and sulfur depending on the petrological type. On this basis, some scientists also divide them into types I (which include E4 and E5) and II (E6). Chondrules in enstatite chondrites are immersed in a dark finely dispersed matrix, have irregular outlines and are filled with debris.

Stone meteorites - achondrites

The next group of stony meteorites, achondrites, include meteorites of asteroid, Martian and Lunar origin. In the course of evolution, they were exposed to high temperatures, which means that at some point they dissolved in magma. When magma cools and crystallizes, it creates concentric layered structures. Generally speaking, achondrite is a stony meteorite that forms from the molten material of its original object of origin; they resemble basalts formed by magmatic processes in the bowels of the Earth. Thus, achondrites have a differentiated structure, having lost a significant part of their original materials, including metals, and, as a rule, do not contain chondrules.

Achondrite slice (photo museum-21.ru)

Planets terrestrial group - Mercury, Venus, Earth and Mars, in the process of formation, formed the planetary crust, mantle and core. Therefore, a stone meteorite in the form of achondrite, such as a meteorite from Mercury, can tell us a lot about the internal structure and formation of planets.

Typical achondritis (photo museum-21.ru)

There are many different groups of achondrites. One of the largest and most famous groups is believed to have originated from the asteroid Vesta,

Iron-stone meteorites

Iron-stone meteorites are divided into two types, differing in chemical and structural properties: palasites and mesosiderites. Pallasites are those meteorites whose silicates consist of magnesian olivine crystals or their fragments enclosed in a continuous matrix of nickel iron. Mesosiderites are called iron-stone meteorites, the silicates of which are mainly recrystallized mixtures of different silicates, also included in the metal cells.

Iron meteorites

Iron meteorites are almost entirely composed of nickel iron and contain small amounts of minerals in the form of inclusions. Iron nickel (FeNi) is a solid solution of nickel in iron. With a high nickel content (30-50%), nickel iron is mainly in the form of tenite (g-phase) - a mineral with a face-centered crystal lattice cell, with a low (6-7%) nickel content in a meteorite, nickel iron consists almost of kamacite (a -phase) - a mineral with a body-centered lattice cell.

Most of the iron meteorites have an amazing structure: they consist of four systems of parallel kamacite plates (differently oriented) with interlayers consisting of tenite, against a background of a fine-grained mixture of kamacite and tenite. The thickness of the kamacite plates can be different - from fractions of a millimeter to a centimeter, but each meteorite has its own plate thickness.

If the polished surface of the cut of an iron meteorite is etched with an acid solution, then its characteristic internal structure in the form of "Widmanstätten figures" will appear (Fig. 3). They are named after A. de Widmanstetten, who first observed them in 1808. Such figures are found only in meteorites and are associated with an unusually slow (over millions of years) cooling process of nickel iron and phase transformations in its single crystals.

Until the early 1950s. iron meteorites were classified solely by their structure. Meteorites with Widmanstätten figures began to be called octahedrites, since the Kamacite plates composing these figures are located in planes forming an octahedron.

Depending on the thickness L of the kamacite plates (which is related to the total nickel content), octahedrites are divided into the following structural subgroups: very coarse-structured (L\u003e 3.3 mm), coarse-structured (1.3< L < 3,3), среднеструкткрные (0,5 < L < 1,3), тонкоструктурные (0,2 < L < 0,5), весьма тонкоструктурные (L < 0,2), плесситовые (L < 0,2).

Some iron meteorites with a low nickel content (6-8%) do not show Widmanstätten patterns. Such meteorites consist, as it were, of a single kamacite single crystal. They are called hexahedrites, since they have a mostly cubic crystal lattice. Sometimes there are meteorites with an intermediate type structure, which are called hexaoctahedrites. There are also iron meteorites that do not have an ordered structure at all - ataxites (in translation "lacking order"), in which the nickel content can vary within wide limits: from 6 to 60%.

The accumulation of data on the content of siderophilic elements in iron meteorites also made it possible to create their chemical classification. If in the n-dimensional space, the axes of which are the contents of different siderophilic elements (Ga, Ge, Ir, Os, Pd, etc.), the positions of different iron meteorites are marked with dots, then the condensation of these points (clusters) will correspond to such chemical groups. Among the almost 500 currently known iron meteorites, 16 chemical groups are clearly distinguished by the content of Ni, Ga, Ge and Ir (IA, IB, IC, IIA, IIB, IIC, IID, IIE, IIIA, IIIB, IIIC, IIID, IIIE, IIIF, IVA, IVB). Since 73 meteorites in this classification turned out to be anomalous (they are classified as a subgroup of unclassified ones), it is believed that there are other chemical groups, perhaps there are more than 50, but they are still underrepresented in collections.

The chemical and structural groups of iron meteorites are not uniquely related. But meteorites from the same chemical group, as a rule, have a similar structure and some characteristic thickness of kamacite plates. Probably, the meteorites of each chemical group were formed under similar temperature conditions, perhaps even in the same parent body.

5. Composition and structure of meteorite matter

Among the meteorite matter falling to the Earth by the number of falls, approximately 92% are stone meteorites, 6% are iron and 2% are iron-stone (or 85, 10 and 5% by mass, respectively).

The atmosphere serves as the first "filter" through which the meteorite material must pass. The more refractory and durable it is, the more chances it has to get to the earth's surface. Another filter is the selection of meteorites when they are found. The more the meteorite stands out against the background of the earth's surface, the easier it is to find it. Thirty years ago, Japanese scientists discovered that Antarctica was the best place to look for meteorites. First, the meteorite is easy to spot in the background. white ice... Secondly, they are better preserved in ice. Meteorites that have fallen elsewhere on the Earth are exposed to atmospheric weathering, water erosion and other destructive factors; therefore, they either decompose or turn out to be buried.

The main components of the meteorite matter are iron-magnesian silicates and nickel iron. Iron sulfides (troilite, etc.) are sometimes abundant. Common minerals included in the silicates of meteorite matter are olivines (Fe, Mg) 2 SiO 4 (from fayalite Fe 2 SiO 4 to forsterite Mg 2 SiO 4) and pyroxenes (Fe, Mg) SiO 3 (from ferrosilite FeSiO 3 to enstatite MgSiO 3) of different composition. They are present in silicates either as fine crystals or glass, or as a mixture with varying proportions. To date, about 300 different minerals have been found in meteorite matter. And although their number gradually increases in the process of researching new meteorites, it is still more than an order of magnitude inferior to the number of known earth minerals.

6. The complex history of meteorite matter

There is another important