Iron meteorites are the most valuable and expensive. Meteorites: types, mineral and chemical composition Meteorite group
A meteorite is a meteorite that has fallen to the planet's surface. solid natural cosmic origin in size from 2 mm. Bodies that have reached the surface of the planet and have sizes from 10 microns to 2 mm are usually called micrometeorites; smaller particles are cosmic dust. Meteorites are characterized by different composition and structure. These features reflect the conditions of their origin and allow scientists to more confidently judge the evolution of the bodies of the solar system.
Types of meteorites by chemical composition and structure
The meteorite substance is mainly composed of mineral and metal components in various proportions. The mineral part is iron-magnesium silicates, the metal part is represented by nickel iron. Some meteorites contain impurities that determine some important features and carrying information about the origin of the meteorite.
How are meteorites classified according to their chemical composition? Traditionally, three large groups are distinguished:
- Stony meteorites are silicate bodies. Among them are chondrites and achondrites, which have important structural differences. So, chondrites are characterized by the presence of inclusions - chondrules - in the mineral matrix.
- Iron meteorites composed predominantly of nickel iron.
- Iron-stone - bodies of an intermediate structure.
In addition to the classification that takes into account chemical composition meteorites, there is also the principle of dividing "heavenly stones" into two broad groups according to structural features:
- differentiated, which include only chondrites;
- undifferentiated - an extensive group that includes all other types of meteorites.
Chondrites - remnants of a protoplanetary disk
Distinctive feature this type of meteorites are chondrules. They are mostly silicate formations of an elliptical or spherical shape, about 1 mm in size. The elemental composition of chondrites is almost identical to the composition of the Sun (if we exclude the most volatile, light elements - hydrogen and helium). Based on this fact, scientists came to the conclusion that chondrites were formed at the dawn of the existence of the solar system directly from the protoplanetary cloud.
These meteorites have never been part of large celestial bodies that have already undergone magmatic differentiation. Chondrites were formed by condensation and accretion of protoplanetary matter, while experiencing some thermal effects. The substance of chondrites is quite dense - from 2.0 to 3.7 g / cm 3 - but fragile: a meteorite can be crushed by hand.
Let's take a closer look at the composition of meteorites of this type, the most common (85.7%) of all.
carbonaceous chondrites
Carbonaceous rocks are characterized by a high content of iron in silicates. Their dark color is due to the presence of magnetite, as well as impurities such as graphite, soot and organic compounds. In addition, carbonaceous chondrites contain water bound in hydrosilicates (chlorite, serpentine).
According to a number of characteristics, C-chondrites are divided into several groups, one of which - CI-chondrites - is of exceptional interest to scientists. These bodies are unique in that they do not contain chondrules. It is assumed that the substance of meteorites of this group was not subjected to thermal impact at all, that is, it remained practically unchanged since the time of condensation of the protoplanetary cloud. These are the oldest bodies in the solar system.
Organics in meteorites
Carbonaceous chondrites contain such organic compounds as aromatic and as well as carboxylic acids, nitrogenous bases (in living organisms they are part of nucleic acids) and porphyrins. Despite the high temperatures that a meteorite undergoes when passing through the earth's atmosphere, hydrocarbons are preserved due to the formation of a melting crust, which serves as a good heat insulator.
These substances, most likely, are of abiogenic origin and indicate the processes of primary organic synthesis already in the conditions of a protoplanetary cloud, given the age of carbonaceous chondrites. So the young Earth already at the earliest stages of its existence had the source material for the emergence of life.
Ordinary and enstatite chondrites
The most common are ordinary chondrites (hence their name). These meteorites contain, in addition to silicates, nickel iron and bear traces of thermal metamorphism at temperatures of 400–950 °C and shock pressures of up to 1000 atmospheres. The chondrules of these bodies are often irregular in shape; they contain detrital material. Ordinary chondrites include, for example, the Chelyabinsk meteorite.
Enstatite chondrites are characterized by the fact that they contain iron mainly in the metallic form, and the silicate component is rich in magnesium (enstatite mineral). This group of meteorites contains less volatile compounds than other chondrites. They underwent thermal metamorphism at temperatures of 600-1000 °C.
Meteorites belonging to both of these groups are often fragments of asteroids, that is, they were part of small protoplanetary bodies in which the processes of interior differentiation did not take place.
Differentiated meteorites
Let us now turn to the consideration of what types of meteorites are distinguished by chemical composition in this vast group.
Firstly, these are stone achondrites, secondly, iron-stone and, thirdly, iron meteorites. They are united by the fact that all representatives of the listed groups are fragments of massive bodies of asteroid or planetary size, the interior of which has undergone differentiation of matter.
Among differentiated meteorites, there are both fragments of asteroids and bodies knocked out from the surface of the Moon or Mars.
Features of differentiated meteorites
Achondrite does not contain special inclusions and, being poor in metal, is a silicate meteorite. In composition and structure, achondrites are close to terrestrial and lunar basalts. Of great interest is the HED group of meteorites, presumably originating from the mantle of Vesta, which is considered to be a preserved terrestrial protoplanet. They are similar to the ultramafic rocks of the Earth's upper mantle.
Stony iron meteorites - pallasite and mesosiderite - are characterized by the presence of silicate inclusions in a nickel iron matrix. Pallasites got their name in honor of the famous Pallas iron found in the 18th century near Krasnoyarsk.
Most iron meteorites are distinguished by an interesting structure - "widmanstetten figures" formed by nickel iron with different nickel content. Such a structure was formed under conditions of slow crystallization of nickel iron.
The history of the substance of "heavenly stones"
Chondrites are messengers from the most ancient era of the formation of the solar system - the time of accumulation of pre-planetary matter and the birth of planetesimals - the embryos of future planets. Radioisotope dating of chondrites shows that their age exceeds 4.5 billion years.
As for differentiated meteorites, they show us the formation of the structure of planetary bodies. Their substance has distinct signs of melting and recrystallization. Their formation could take place in different parts a differentiated parent body, which subsequently underwent complete or partial destruction. This determines what chemical composition of meteorites, what structure formed in each case, and serves as the basis for their classification.
Differentiated celestial guests also contain information about the sequence of processes that took place in the depths of the parent bodies. Such, for example, are iron-stone meteorites. Their composition testifies to the incomplete separation of the light silicate and heavy metal components of the ancient protoplanet.
In the processes of collision and crushing of asteroids different types and ages in the surface layers of many of them, the accumulation of mixed fragments of various origins could occur. Then, as a result of a new collision, a similar “composite” fragment was knocked out from the surface. An example is the Kaidun meteorite containing particles of several types of chondrites and metallic iron. So the history of meteorite matter is often very complex and confusing.
At present, much attention is paid to the study of asteroids and planets with the help of automatic interplanetary stations. Of course, it will contribute to new discoveries and a deeper understanding of the origin and evolution of such witnesses to the history of the solar system (and our planet as well) as meteorites.
> Types of meteorites
Find out what are types of meteorites: classification description with photo, iron, stone and stone-iron, meteorites from the Moon and Mars, asteroid belt.
Often a common person imagining what a meteorite looks like, thinks of iron. And it's easy to explain. Iron meteorites are dense, very heavy, and often take on unusual and even impressive shapes as they fall and melt in our planet's atmosphere. And although iron is associated with the typical composition of space rocks in most people, iron meteorites are one of the three main types of meteorites. And they are quite rare compared to stony meteorites, especially the most common group of them - single chondrites.
Three main types of meteorites
There is a large number meteorite types, divided into three main groups: iron, stone, stone-iron. Almost all meteorites contain extraterrestrial nickel and iron. Those that do not contain iron at all are so rare that even if we ask for help identifying possible space rocks, we will most likely 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 contained in the sample.
iron type meteorite
iron meteoriteswere part of the core of a long-dead planet or a large asteroid from which it is believed that between Mars and Jupiter. They are the densest materials on Earth and are very strongly 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 I'm talking about.
In most samples of this group, the iron component is approximately 90% -95%, the rest is nickel and trace elements. Iron meteorites are divided into classes according to their chemical composition and structure. Structural classes are determined by examining two components of iron-nickel alloys: kamacite and taenite.
These alloys have a complex crystal structure known as the Widmanstetten 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 the iron meteorite is cut into plates, polished and then etched in a weak solution of nitric acid. For kamacite crystals found in the process, the average band width is measured and the resulting figure is used to separate iron meteorites into structural classes. Iron with a thin band (less than 1 mm) is called "fine-structured octahedrite", with a wide band "coarse octahedrite".
Stone view of the meteorite
The largest group of meteorites - stone, they formed from the outer crust of a planet or asteroid. Many stony meteorites, especially those that have been on the surface of our planet for a long time, are very similar to ordinary terrestrial stones, and it takes an experienced eye to find such a meteorite in the field. Recently fallen rocks have a black lustrous surface that was formed by the burning of the surface in flight, and the vast majority of rocks 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, before the formation of our planet and the entire solar system, which makes them the oldest known matter available for study. Stony meteorites containing these chondrules are called "chondrites".
Space rocks without chondrules are called "achondrites". These are volcanic rocks, shaped by volcanic activity on their "parent" space objects, where melting and recrystallization have obliterated all traces of the ancient chondrules. Achondrites contain little or no iron, making it difficult to find compared to other meteorites, although specimens often have a glossy crust that looks like enamel paint.
Stone view of a meteorite 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 about thirty Martian meteorites have been found on Earth, and all of them belong to the achondrite group.
The collision of the surface of the Moon and Mars with other meteorites threw fragments into outer space and some of them fell to the ground. From a financial point of view, lunar and Martian samples are among the most expensive meteorites. In the collectors' markets, they cost up to a thousand dollars per gram, which makes them several times more expensive than if they were made of gold.
Stone-iron type of meteorite
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: pallasite and mesosiderite. Stone-iron meteorites were formed at the border of the crust and mantle of their "parent" bodies.
Pallasites are perhaps the most enticing of all meteorites and are definitely of great interest to private collectors. Pallasite is composed of an iron-nickel matrix filled with olivine crystals. When olivine crystals are clear enough to appear emerald green, they are known as a perodot gemstone. 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 slabs and polished, it becomes translucent, giving it an ethereal beauty.
Mesosiderites are the smaller of the two stony-iron groups. They are composed of iron-nickel and silicates and are usually attractive. The high contrast of the silver and black matrix, when the plate is cut and sanded, and the occasional blotch, results in a very unusual look. The word mesosiderite comes from the Greek for "half" and "iron" and they are very rare. In thousands of official catalogs of meteorites, there are less than a hundred mesosiderites.
Classification of types of meteorite
Meteorite classification is a complex and technical subject and the above is only intended as a brief overview of the topic. Classification methods have changed several times over the years. last years; known meteorites were reclassified to another class.
Most iron meteorites are fairly resistant to terrestrial weathering, allowing them to survive much longer than any other type of meteorite. This means that the price for such meteorites will be somewhat higher than for ordinary chondrites.
Iron meteorites tend to be much larger than stony or stony-iron meteorites. Iron meteorites rarely change shape when entering the atmosphere and suffer much less ablation effects 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. Among the found meteorites, they occur only in 5.7% of cases.
Iron meteorites are composed mainly of iron and nickel. Most of them include only minor impurities of minerals. These additional minerals often occur in round nodules that are composed of iron sulfide, troilite or graphite, often surrounded by iron phosphide schreibersite and iron carbide cohenite. Classic example- the Campo del Cielo meteorite, the Willamette meteorite, or the Cape York meteorite. Despite the fact that some iron meteorites contain silicate inclusions, most of them are similar in appearance.
Currently, iron meteorites are classified according to two established systems. Just a few decades ago, iron meteorites were classified according to their macroscopic structure when their polished surfaces were treated nitric acid. Currently, a 5% solution of nitric acid in alcohol is used for these purposes.
Besides, modern research very sophisticated instruments are used that allow us to detect even minute amounts of elements such as germanium, gallium or iridium. Based on the specific concentration of these elements and their correlation with the total nickel content, iron meteorites are classified into several chemical groups, and each group is believed to represent a unique "fingerprint" of the parent body from which the meteorite originated.
Iron and nickel occur in iron meteorites as two different minerals. The most common mineral is kamacite. Kamacite contains 4% to 7.5% nickel and forms large crystals that appear as wide bands or ray-like structures on the etched surface of an iron meteorite. Another mineral is called taenite.
Taenite contains 27% to 65% nickel, and it usually forms smaller crystals that appear as reflective thin ribbons on the etched surface of an iron meteorite. Depending on the occurrence and presence of these nickel-iron minerals, iron meteorites are classified into three main classes: octahedrite, hexahedrite, and ataxite.
Octahedrites
The most common display structure on the etched surface of iron meteorites is the intergrowth of kamacite and taenite in lamellae that intersect each other at different angles. These patterns of intersecting stripes and ribbons are called "Widmanstetten figures" after their discoverer, Alois von Widmanstetten.
They show the intergrowth of kamacite and taenite into plates. This accretion has a spatial arrangement in the form of an octahedron, and therefore these iron meteorites are called octahedrites. The space between the plates of kamacite and taenite is often filled with a fine-grained mixture called plessite.
Hexahedrites
Hexahedrites are composed mainly of kamacite. They got their name from the shape of the crystal structure of kamacite - a hexagon. The purest form of kamacite is a cubic crystal with six equal parties at right angles to each other.
After etching with nitric acid, hexahedrites do not show Widmanstätten figures, but they often show parallel lines called "Neumann Lines" (discoverer Franz Ernst Neumann, who first studied them in 1848).
Ataxites
Some iron meteorites do not show a clear internal structure when etched, and they are called ataxites. Ataxites consist mainly of nickel-rich taenite and kamacite. It occurs only in the form of microscopic lamellas and spindles. Consequently, ataxites represent the most nickel-rich iron meteorites and are among the rarest types of meteorites. Paradoxically, the largest meteorite found on Earth, known as Goba, belongs to this rare structural class.
Meteorite- this is a solid extraterrestrial substance that was preserved during the passage through the atmosphere and reached the surface of the Earth. Meteorites are the most primitive of the SS, which have not experienced further fractionation since their formation. This is based on the fact that the relative distribution refractory el. in meteorites corresponds to the solar distribution. Meteorites are classified into (according to the content of the metal phase): Stone(aeroliths): achondrites, chondrites, iron stone(siderolites), iron(siderites). Iron meteorites - consist of kamacite - native Fe of cosmic origin with an admixture of nickel from 6 to 9%. Iron stone meteorites Small distribution group. They have coarse-grained structures with equal weight proportions of silicate and Fe phases. (Silicate minerals - Ol, Px; Fe phase - kamacite with Widmanstätten intergrowths). Stone meteorites - consist of silicates of Mg and Fe with an admixture of metals. Subdivided into Chondrite, achondrite and carbonaceous.Chondrites: spheroidal segregations of the first mm or less in size, composed of silicates, less often silicate glass. Embedded in a Fe-rich matrix. The groundmass of chondrites is a fine-grained mixture of Ol, Px (Ol-bronzite, Ol-hypersthene and Ol-pijonitic) with nickel Fe (Ni-4-7%), troilite (FeS) and plagioclase. Chondrites - crystallized. or glassy drops, cat. Image. when melting a pre-existing silicate material subjected to heating. Achondrites: Do not contain chondrules, have a lower content. nickel Fe and coarser structures. Their main minerals are Px and Pl, some types are enriched in Ol. In composition and structural features, achondrites are similar to terrestrial Gabbroids. The composition and structure speak of a magmatic origin. Sometimes there are bubbly structures like lavas. Carbonaceous chondrites (large amounts of carbonaceous matter) Characteristic feature of carbonaceous chondrites - the presence of a volatile component, which indicates primitiveness (the removal of volatile elements did not occur) and did not undergo fractionation. Type C1 contains a large number of chlorite(aqueous Mg, Fe aluminosilicates), as well as magnetite, water-soluble salt, nativeS, dolomite, olivine, graphite, organ. connections. Those. since their image-I they are noun. at T, not > 300 0 С. chondrite meteorites lack of 1/3 chem. Email compared to composition carbonaceous chondrites, cat. closest to the composition of protoplanetary matter. The most likely cause of the shortage of volatile email. - sequential condensation el. and their compounds in reverse order of their volatility.
5.Historical and modern models of accretion and differentiation of protoplanetary matter O.Yu. Schmidt in the 40s expressed the idea that the Earth and the planets of the CG were formed not from hot clots of solar gases, but through the accumulation of HB. bodies and particles - planetesimals that experienced melting later during accretion (heating due to collisions of large planetesimals, up to a few hundreds of kilometers in diameter). Those. early differentiation of the core and mantle and degassing. Ex. relates two points of view. accumulation mechanism and ideas about the form of the layered structure of the planets. Models homogeneous and heterogeneous accretion: HETEROGENEOUS ACCRETION 1. Short-term accretion. Early heterogeneous accretion models(Turekian, Vinogradov) assumed that Z. accumulated from the material as it condensed from the protoplanetary cloud. Early models include an early > T accumulation of the Fe-Ni alloy, which forms the proto-core of Z., changing from lower. T by accretion of its outer parts from silicates. Now it is believed that in the process of accretion there is a continuous change. in the accumulating material of the Fe/silicate ratio from the center to the periphery of the formed planet. As the earth accumulates, it heats up and melts Fe, which separates from the silicates and sinks into the core. After the cooling of the planet, about 20% of its mass is added with material enriched in volatiles along the periphery. In the proto-earth, there were no sharp boundaries between the core and the mantle, a cat. established as a result of gravitation. and chem. differentiation at the next stage of the evolution of the planet. In the early versions, differentiation occurred mainly during the formation of the ZK, and did not capture the Earth as a whole. HOMOGENEOUS ACCRETION 2. A longer accretion time of 108 years is assumed. During the accretion of the Earth and the planets of the Earth, the condensing bodies had wide variations in composition from carbonaceous chondrites enriched in volatiles to substances enriched in refractory components of the Allende type. Planets of forms. from this set of meteorites in-va and their difference and similarity was determined by relative. proportions in-va different composition. It also took place macroscopic homogeneity of protoplanets. The existence of a massive core indicates that the alloy originally introduced by Fe-Ni meteorites, uniformly distributed throughout the Earth, separated out in the course of its evolution into the central part. Homogeneous in composition the planet was stratified into shells in the process of gravitational differentiation and chemical processes. Modern model of heterogeneous accretion to explain the chem. the composition of the mantle is being developed by a group of German scientists (Wencke, Dreybus, Yagoutz). They found that the content in the mantle of moderately volatile (Na, K, Rb) and moderately siderophilic (Ni, Co) el., with different. The distribution coefficients of Me/silicate have the same abundance (normalized by C1) in the mantle, and the most strongly siderophile elements have excess concentrations. Those. the core was not in equilibrium with the mantle reservoir. They proposed heterogeneous accretion :1. Accretion begins with the accumulation of a strongly reduced component A, devoid of volatile elements. and containing all the other email. in quantities corresponding to C1, and Fe and all siderophiles in the reduced state. With an increase in T, the formation of a nucleus begins simultaneously with accretion. 2. After accretion, more and more oxidized material, component B, begins to accumulate in 2/3 of the earth's mass. and transfer them to the kernel. A source of moderately volatile, volatile and moderately siderophilic el. in the mantle yavl. component B, which explains their close relative abundance. Thus, the Earth is 85% composed of component A and 15% of component B. In general, the composition of the mantle is formed after separation of the core by homogenization and mixing of the silicate part of component A and the substance of component B.
6. Isotopes of chemical elements. isotopes - atoms of the same electron, but having a different number of neutrons N. They differ only in mass. isotons - atoms of different el., having different Z, but the same N. They are arranged in vertical rows. isobars - atoms of different el., in a cat. equal masses. numbers (A=A), but different Z and N. They are arranged in diagonal rows. Nuclear stability and isotope abundance; radionuclides The number of known nuclides is ~ 1700, of which ~ 260 are stable. On the nuclide diagram, stable isotopes (shaded squares) form a band surrounded by unstable nuclides. Only nuclides with a certain ratio of Z and N are stable. The ratio of N to Z increases from 1 to ~ 3 with increasing A. 1. Nuclides are stable, in a cat. N and Z are approximately equal. Up to Ca in N=Z nuclei. 2. Most stable nuclides have even Z and N. 3. Less common are stable nuclides with even numbers. Z and odd. N or even N and odd. Z. 4. Rare stable nuclides with odd Z and N.
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In kernels from even. Z and N nucleons form an ordered structure, which determines their stability. The number of isotopes is less in light email. and took away. in the middle part of the PS, reaching a maximum for Sn (Z=50), which has 10 stable isotopes. Elements with odd. Z stable isotopes no more than 2.
7. Radioactivity and its types Radioactivity - spontaneous transformations of the nuclei of unstable atoms (radionuclides) into stable nuclei of other elements, accompanied by emission of particles and/or radiation of energy. St. glad-ti does not depend on the chemical. Holy atoms, but determined by the structure of their nuclei. Radioactive decay is accompanied by changes. Z and N of the parent atom and leads to the transformation of an atom of one el. into an atom of another email. It has also been shown by Rutherford and other scientists that he is glad. the decay is accompanied by the emission of radiation of three different types, a, b, g. a - rays - streams of high-speed particles - He nuclei, b - rays - streams e - , g - rays - electromagnetic waves with high energy and shorter λ. Types of radioactivity a-decay- decay by emission of a-particles, it is possible for nuclides with Z> 58 (Ce), and for a group of nuclides with small Z, including 5He, 5Li, 6Be. a-particle consists of 2 P and 2N, there is a shift of 2 positions in Z. The initial isotope is called parental or maternal, and the newly formed - child.
b-decay- has three types: normal b-decay, positron b-decay and e - capture. Ordinary b-decay- can be considered as the transformation of a neutron into a proton and e - , the last or beta particle - is ejected from the nucleus, accompanied by the emission of energy in the form of g-radiation. The daughter nuclide is an isobar of the parent, but its charge is greater.
There is a series of decays until a stable nuclide is formed. Example: 19 K40 -> 20 Ca40 b - v - Q. Positron b-decay- emission from the nucleus of a positive particle of a positron b, its formation - the transformation of a nuclear proton into a neutron, positron and neutrino. The daughter nuclide is an isobar but has a smaller charge.
Example, 9 F18 -> 8 O18 b v Q while the number N decreases. Atoms to the left of the region of nuclear stability are neutron-deficient, they undergo positron decay, and their number N increases. Thus, during b- and b-decay, there is a tendency for Z and N to change, leading to the approach of daughter nuclides to the zone of nuclear stability. e – capture- capture of one of the orbital electrons. High probability of capture from the K-shell, cat. closest to the core. e - capture causes emission from the neutrino nucleus. Daughter nuclide yavl. isobar, and occupies the same position relative to the parent as in positron decay. b - radiation is absent, and when a vacancy is filled in the K-shell, X-rays are emitted. At g radiation neither Z nor A change; when the nucleus returns to its normal state, energy is released in the form g-radiation. Some daughter nuclides of the natural isotopes U and Th can decay either by emitting b-particles or by a-decay. If b-decay occurred first, then a-decay followed, and vice versa. In other words, these two alternative species decays form closed cycles and always lead to the same end product - stable isotopes of Pb.
8. Geochemical consequences of the radioactivity of terrestrial matter. Lord Kelvin (William Thomson) from 1862 to 1899 performed a series of calculations, cat. imposed restrictions on the possible age of the Earth. They were based on consideration of the luminosity of the Sun, the influence of lunar tides, and the processes of cooling of the Earth. He came to the conclusion that the age of the Earth is 20-40 million years. Later, Rutherford performed the determination of the age of U min. and received values of about 500 million years. Later, Arthur Holmes in his book "The Age of the Earth" (1913) showed the importance of the study of radioactivity in geochronology and gave the first GHS. It was based on consideration of data on the thickness of sedimentary deposits and on the content of radiogenic decay products - He and Pb in U-bearing minerals. Geological scale- the scale of the natural historical development of the ZK, expressed in numerical units of time. The accretion age of Earth is about 4.55 billion years. The period up to 4 or 3.8 billion years is the time of differentiation of the planetary interior and the formation of the primary crust, it is called katarchey. The longest period of life of Z. and ZK is the Precambrian, cat. extends from 4 billion years to 570 million years, i.e. about 3.5 billion years. The age of the most ancient rocks known now exceeds 4 billion years.
9. Geochemical classification of elements by V.M. HolshmidtBased on: 1- distribution email. between different phases of meteorites - separation during the primary HX differentiation of Z. 2 - specific chemical affinity with certain elements (O, S, Fe), 3 - structure of electron shells. The leading elements that make up meteorites are O, Fe, Mg, Si, S. Meteorites consist of three main phases: 1) metal, 2) sulfide, 3) silicate. All e-mail are distributed between these three phases in accordance with their relative affinity for O, Fe and S. In the Goldschmidt classification, the following groups of elec. are distinguished: 1) siderophilic(loving iron) - metal. phase of meteorites: el., forming alloys of arbitrary composition with Fe - Fe, Co, Ni, all platinoids (Ru, Rh, Pd, Pt, Re, Os, Ir), and Mo. They often have a native state. These are transition elements. group VIII and some of their neighbors. Form the inner core Z. 2) Chalcophilic(copper-loving) - the sulfide phase of meteorites: elements that form natural compounds with S and its analogues Se and Te also have an affinity for As (arsenic), sometimes they are called (sulfurophilic). Easily pass into a native state. These are elements of secondary subgroups I-II and main subgroups III-VI groups of PS from 4 to 6 period S. The most famous are Cu, Zn, Pb, Hg, Sn, Bi, Au, Ag. Siderophile el. – Ni, Co, Mo can also be chalcophilic with a large amount of S. Fe under reducing conditions has an affinity for S (FeS2). In the modern model of the star, these metals form the outer, sulfur-enriched core of the star.
3) lithophilic(loving stone) - silicate phase of meteorites: el., having an affinity for O 2 (oxyphilic). They form oxygen compounds - oxides, hydroxides, salts of oxygen acids-silicates. In compounds with oxygen, they have an 8-electron ext. shell. This is the most numerous group of 54 elements (C, widespread petrogenic - Si, Al, Mg, Ca, Na, K, elements of the iron family - Ti, V, Cr, Mn, rare - Li, Be, B, Rb, Cs, Sr , Ba, Zr, Nb, Ta, REE, i.e. all the rest except atmophilic ones). Under oxidizing conditions, iron is oxyphilic - Fe2O3. form the mantle Z. 4) Atmophilic(har-but gaseous state) - chondrite matrix: H, N inert gases (He, Ne, Ar, Kr, Xe, Rn). They form the atmosphere Z. There are also such groups: rare earth Y, alkaline, large-ion lithophile elements LILE (K, Rb, Cs, Ba, Sr), highly charged elements or elements with high field strength HFSE (Ti, Zr, Hf, Nb, Ta , Th). Some definitions of email: petrogenic (rock-forming, main) minor, rare, trace elements- with conc. no more than 0.01%. scattered- microel. not forming their own minerals accessory- form accessory min. ore- form ore mines.
10. The main properties of atoms and ions that determine their behavior in natural systems. Orbital radii - radii of the maxima of the radial density e – ext. orbitals. They reflect the sizes of atoms or ions in the free state, i.e. outside the chem. connections. The main factor is e - the structure of the electron, and the more e - shells, the larger the size. For def. sizes of atoms or ions in an important way yavl. Def. distance from the center of one atom to the center of another, cat. is called the bond length. For this, X-ray methods are used. In the first approximation, atoms are considered as spheres, and the “principle of additivity” is applied, i.e. it is believed that the interatomic distance is the sum of the radii of the atoms or ions that make up the in-in. Then knowing or accepting a certain value as the radius of one el. you can calculate the dimensions of all others. The radius calculated in this way is called effective radius . coordination number is the number of atoms or ions located in close proximity around the considered atom or ion. CF is determined by the ratio R k /R a: Valence - the amount of e - given or attached to the atom during the formation of chemical. connections. Ionization potential is the energy required to remove e- from an atom. It depends on the structure of the atom and is determined experimentally. The ionization potential corresponds to the voltage of the cathode rays, which is sufficient to ionize an atom of this email. There may be several ionization potentials, for several e - removed from the external. e - shells. The separation of each subsequent e - requires more energy and may not always be. Usually use the ionization potential of the 1st e - , cat. detects periodicity. On the curve of ionization potentials, alkali metals, which easily lose e - , occupy minima on the curve, inert gases - peaks. As the atomic number increases, the ionization potentials increase in the period and decrease in the group. The reciprocal is the affinity ke – . Electronegativity - the ability to attract e - when entering into compounds. The halogens are the most electronegative, the alkali metals the least. Electronegativity depends on the charge of the nucleus of an atom, its valency in a given compound, and the structure of the e-shells. Repeated attempts have been made to express EC in units of energy or in conventional units. The values of EC regularly change by groups and periods of PS. EO are minimal for alkali metals and increase towards halogens. In lithophilic cations, EO is reduced. from Li to Cs and from Mg to Ba, i.e. with a zoom ionic radius. In chalcophile el. EO is higher than that of lithophiles from the same PS group. For anions of the O and F groups, the EO decreases down the group and, therefore, it is maximum for these el. Email with sharply different values of EO form compounds with an ionic type of bond, and with close and high values - with a covalent type, with close and low values - with a metallic type of bond. The ionic potential of Cartledge (I) is equal to the ratio of valence to R i , it reflects the properties of cationicity or ionogenicity. V.M. Golshmidt showed that the properties of cationicity and anionicity depend on the ratio of valence (W) and R i for ions of the noble gas type. In 1928, K. Cartledge called this ratio the ionic potential I. At small values of I el. behaves like a typical metal and cation (alkali and alkaline earth metals), and at large - like a typical non-metal and anion (halogens). These relationships are conveniently depicted graphically. Diagram: ionic radius - valency. The value of the ionic potential allows us to judge the mobility of email. in the aquatic environment. Email with low and high values of I are the most mobile easily (with low values they pass into ionic solutions and migrate, with high values they form complex soluble ions and migrate), and with intermediate ones they are inert. The main types of chem. bonds, character bonds in the main groups of minerals. Ionic- image due to the attraction of ions with opposite charges. (with a large difference in electronegativity) Ionic bonding predominates in most mines. ZK - oxides and silicates, this is the most common type of bond also in hydro and atmospheres. Communication provides easy dissociation of ions in melts, solutions, gases, due to which there is a wide migration of chemical. El., their dispersion and end in the terrestrial geospheres. covalent - noun. due to the interaction e - used by different atoms. Typical for e. with an equal degree of attraction e – , i.e. EO. Har-na for liquid and gaseous substances (H2O, H2, O2, N2) and less for a crystal. Sulfides, related compounds As, Sb, Te, as well as monoel are characterized by a covalent bond. non-metal compounds - graphite, diamond. Covalent compounds are characterized by low solubility. metal- a special case covalent bond, when each atom shares its e - with all neighboring atoms. e - capable of free movement. Typical for native metals (Cu, Fe, Ag, Au, Pt). Many min. have a connection, a cat. partly ionic, partly covalent. in sulfide mines. the covalent bond is maximally manifested, it takes place between the metal and S atoms, and the metallic one - between the metal atoms (metal, brilliance of sulfides). Polarization - this is the effect of distortion of the e-cloud of an anion by a small cation with a large valence, so that a small cation, attracting a large anion to itself, reduces its effective R, itself entering its e-cloud. So the cation and anion are not regular spheres, and the cation causes the deformation of the anion. The higher the charge of the cation and the smaller its size, the stronger the effect of polarization. And the larger the size of the anion and its negative charge, the stronger it is polarized - deformed. Lithophilic cations (with 8 electron shells) cause less polarization than ions with completed shells (like Fe). Chalcophile ions with large serial numbers and high-valent cause the strongest polarization. This is associated with the formation of complex compounds: 2-, , 2-, 2-, cat. soluble and yavl. the main carriers of metals in hydrothermal solutions.
11.Status (form of location) email. in nature. In GC allocate: actually min. (crystal. phases), impurities in min., various forms of the scattered state; email location form in nature carries information about the degree of ionization, har-re chem. email connections in phases, etc. V-in (el.) is in three main forms. The first is the end atoms, the image. stars are different. types, gaseous nebulae, planets, comets, meteorites and space. tv. particles in-va. Degree of conc. V-va in all bodies is different. The most scattered states of atoms in gaseous nebulae are held by gravitational forces or are on the verge of overcoming them. The second - scattered atoms and molecules, an image of interstellar and intergalactic gas, consisting of free atoms, ions, molecules, e -. Its quantity in our Galaxy is much less than that which is concentrated in stars and gaseous nebulae. Interstellar gas is located at different sparse stages. The third - intensively migrating, flying with tremendous speed atomic nuclei and elementary particles that make up cosmic rays. IN AND. Vernadsky singled out the main four forms of finding chem. Email in the ZK and on its surface: 1. rocks and minerals (solid crystalline phases), 2. magmas, 3. scattered state, 4. living matter. Each of these forms is distinguished by the special state of their atoms. Ex. and other allocation of forms of finding e-mail. in nature, depending on the specific sv-in themselves email. A.I. Perelman singled out mobile and inert forms finding chem. Email in the lithosphere. By his definition, movable form is such a state of chemistry. Email in gp, soils and ores, being in a cat. Email can easily pass into the solution and migrate. inert form represents such a state in urban settlements, ores, weathering crust and soils, in the cat. Email under the conditions of this situation, it has a low migratory mode and cannot move into the solution and migrate.
12. Internal factors of migration.
Migration- movement of chemicals Email in geospheres Z, leading to their dispersion or conc. Clarke - medium conc. in the main types of GP ZK of each chem. Email can be considered as a state of its equilibrium under the conditions of a given chemical. Wednesdays, a deviation from a cat. gradually reduced by migrating this email. Under terrestrial conditions, the migration of chemical Email happens in any medium - TV. and gaseous (diffusion), but easier in a liquid medium (in melts and aqueous solutions). At the same time, the forms of migration of chemical Email are also different - they can migrate in atomic (gases, melts), ionic (solutions, melts), molecular (gases, solutions, melts), colloidal (solutions) forms and, in the form of detrital particles (air and water environment ). A.I. Perelman distinguishes four types of chemical migration. El.: 1.mechanical, 2.phys.-chemical, 3.biogenic, 4.technogenic. The most important internal factors: 1. Thermal properties of electricity, i.e. their volatility or infusibility. El., having a condensation T of more than 1400 o K are called refractory platinoids, lithophilic - Ca, Al, Ti, Ree, Zr, Ba, Sr, U, Th), from 1400 to 670 o K - moderately volatile. [lithophile - Mg, Si (moderately refractory), many chalcophile, siderophile - Fe, Ni, Co],< 670 o K – летучими (атмофильные). На основании этих св-в произошло разделение эл. по геосферам З. При магм. процессе в условиях высоких Т способность к миграции будет зависеть от возможности образования тугооплавких соединений и, нахождения в твердой фазе. 2. Хим. Св-ва эл. и их соединений. Атомы и ионы, обладающие слишком большими или слишком малыми R или q, обладают и повышенной способностью к миграции и перераспределению. Хим. Св-ва эл. и их соединений приобретают все большее значение по мере снижения T при миграции в водной среде. Для литофильных эл. с низким ионным потенциалом (Na, Ca, Mg) в р-рах хар-ны ионные соединения, обладающие высокой раствор-ю и высокими миграционными способностями. Эл. с высокими ионными потенциалами образуют растворимые комплексные анионы (С, S, N, B). При низких Т высокие миграционные способности газов обеспечиваются слабыми молекулярными связями их молекул. Рад. Св-ва, опред-ие изменение изотопного состава и появление ядер других эл.
What is meteoric iron? How does it appear on Earth? You will find answers to these and other questions in the article. Meteoritic iron is a metal found in meteorites and consisting of several mineral phases: taenite and kamacite. It makes up the majority of metallic meteorites, but is also found in other types. Consider meteoric iron below.
Structure
When a polished cut is etched, the structure of meteorite iron appears in the form of the so-called Widmanstätten figures: intersecting beams-strips (kamacite) bordered by shiny narrow ribbons (taenite). Sometimes you can see polygonal fields-platforms.
A fine-grained mixture of taenite and kamacite forms plessite. The iron we are considering in meteorites of the hexahedrite type, which is almost completely composed of kamacite, forms a structure in the form of parallel thin lines, called non-man.
Application
In ancient times, people did not know how to make metal from ore, so meteorite iron was its only source. It has been proven that elementary tools from this substance (identical in shape to stone ones) were created as early as the Bronze Age and the Neolithic. A dagger found in the tomb of Tutankhamen and a knife from the Sumerian town of Ur (about 3100 BC) were made from it, beads found 70 km from Cairo, in places of eternal rest, in 1911 (about 3000 BC). n. e.).
Tibetan sculpture has also been created from this substance. It is known that the king Ancient Rome) was a metal shield made from "a stone that fell from the sky." In 1621, for Jahangir (the ruler of an Indian principality), a dagger, two sabers and a spearhead were forged from heavenly iron.
A saber made of this metal was presented to Tsar Alexander I. According to legend, Tamerlane's swords also had cosmic origin. Today, heavenly iron is used in jewelry production, but most of it is used for scientific experiments.
meteorites
Meteorites are 90% metal. Therefore, the first person began to use heavenly iron. How to distinguish it from the earth? This is very easy to do, because it contains about 7-8% nickel impurities. It is not for nothing that in Egypt it was called stellar metal, and in Greece - heavenly. This substance was considered very rare and expensive. It's hard to believe, but it was previously framed in gold frames.
Stellar iron is not resistant to corrosion, so products made from it are rarely found: they simply could not survive to this day, as they crumbled from rust.
According to the method of detection, iron meteorites are divided into falls and finds. Falls are called such meteorites, the decline of which was visible and which people were able to find shortly after they landed.
Finds are meteorites found on the surface of the Earth, but no one observed their fall.
meteorites falling
How does a meteorite fall to Earth? Over 1,000 falls recorded today heavenly wanderers. This list includes only meteors whose passage through the earth's atmosphere was recorded by automatic equipment or observers.
Star rocks enter our planet's atmosphere at a speed of about 11-25 km/s. At this speed, they begin to warm up and glow. Due to ablation (charring and blowing off by a counter flow of particles of the meteorite substance), the weight of a body that has reached the Earth's surface can be less, and sometimes significantly less than its mass at the entrance to the atmosphere.
The fall of a meteorite to Earth is an amazing phenomenon. If the meteorite body is small, then at a speed of 25 km / s it will burn without residue. As a rule, out of tens and hundreds of tons of primary mass, only a couple of kilograms and even grams of substance reach the earth. Traces of combustion of celestial bodies in the atmosphere can be found throughout almost the entire trajectory of their fall.
The fall of the Tunguska meteorite
This mysterious event happened in 1908, on June 30th. How did the fall of the Tunguska meteorite occur? The celestial body fell in the Podkamennaya area at 7:15 a.m. local time. It was early in the morning, but we were already awake a long time ago. They were doing current affairs, which in the village courtyards require unceasing attention from the very sunrise.
The Podkamennaya Tunguska itself is a full-flowing and mighty river. It flows on the lands of the present Krasnoyarsk Territory, and originates in the Irkutsk region. It makes its way through the taiga wilderness areas, replete with wooded high banks. This is a godforsaken land, but it is rich in minerals, fish and, of course, impressive hordes of mosquitoes.
The mysterious event began at 6:30 local time. Residents of villages located along the banks of the Yenisei saw a fireball of impressive size in the sky. It moved from south to north, and then disappeared over the taiga. At 07:15 a bright flash lit up the sky. After a while there was a terrible roar. The earth shook, glass flew out of the windows in the houses, the clouds turned red. They kept that color for a couple of days.
Observatories located in different parts of the planet recorded a blast wave of great strength. Next, people wanted to know what happened and where. It is clear that in the taiga, but it is very large.
It was not possible to organize a scientific expedition, since there were no rich patrons who were ready to pay for such research. Therefore, scientists first decided only to interview eyewitnesses. They talked with Evenks and Russian hunters. They said that at first a strong wind blew and a loud whistle was heard. Further, the sky was filled with red light. After a thunderclap was heard, trees began to light up and fall. It got very hot. After a couple of seconds, the sky shone even more strongly, and the thunder rang out again. A second sun appeared in the sky, which was much brighter than the usual luminary.
These indications were all limited. The scientists decided that Siberian taiga meteorite fell. And since he landed in the zone of Podkamennaya Tunguska, they called him Tunguska.
The first expedition was equipped only in 1921. Its initiators were academicians Fersman Alexander Evgenievich (1883-1945) and Vernadsky Vladimir Ivanovich (1863-1945). This journey was led by Kulik Leonid Alekseevich (1883-1942), the leading specialist of the USSR on meteorites. Then several more scientific campaigns were organized in 1927-1939. As a result of these studies, the assumptions of scientists were confirmed. In the basin of the Tunguska Podkamennaya River, a meteorite fell indeed. But the huge crater that the fallen body was supposed to create was not discovered. They did not find any crater at all, even the smallest one. But they found the epicenter of a powerful explosion.
It was installed on trees. They stood there as if nothing had happened. And around them, in a radius of 200 km, there was a fallen forest. The surveyors decided that the explosion happened at an altitude of 5-15 km above the ground. In the 60s, it was established that the force of the explosion was equal to the power of a hydrogen bomb with a capacity of 50 megatons.
Today 'bout the fall of this celestial body There are a huge number of assumptions and theories. The official verdict says that it was not a meteorite that fell to Earth, but a comet - a block of ice interspersed with tiny solid cosmic particles.
Some researchers believe that our planet crashed spaceship aliens. In general, almost nothing is known about the Tunguska meteorite. No one can name the parameters and mass of this stellar body. The prospectors will probably never come to the only true concept. After all, how many people, so many opinions. Therefore, the riddle of the Tungus guest will give birth to more and more new hypotheses.
