Some people use the phrase "meteorites are inherently magnetic" to generalize all kinds of meteorites, but they don't summarize and classify all kinds of rich, weak or nonmagnetic meteorites in detail, and don't fully understand the physical and chemical characteristics of all kinds of meteorites. In the folk, we find that many people mistakenly think that meteorites must be magnetic and stones may be meteorites as long as they are magnetic, but they have not made clear the ethnic groups and types of meteorites with and without magnetism. As a result, when many people find that some external features are similar to meteorites, they will take small magnets to test whether there is magnetism on the stones. Many people also habitually classify magnetic stones as suspected meteorites, and throw away those without magnetism as garbage. This absurd behavior of judging and distinguishing between magnetic and nonmagnetic meteorites leads to some rare weakly magnetic and nonmagnetic meteorites being thrown away in vain, especially some aspheric meteorites such as Martian meteorites and lunar meteorites, which are easily thrown away as garbage. Whether meteorites contain magnetic minerals depends on their types. Because both iron meteorites and stone iron meteorites contain certain magnetic metal minerals, and most of them have certain magnetic adsorption. Many chondrites also contain a small amount of metallic substances, but their magnetic adsorption is relatively weak. Some chondrites that have fallen to the surface for a long time and are severely weathered will gradually weaken their magnetic adsorption because some metal substances are replaced by oxides.
Some meteorite lovers, who lack the knowledge of meteorite identification, can also conduct preliminary tests with magnets after discovering suspected iron meteorites or stone iron meteorites. The purpose of the test is to preliminarily judge whether the magnetic metal content is large or not. If it is magnetic, it may be a suspected iron meteorite; If it is medium magnetic, it may be a suspected stone iron meteorite; If it is weak, it may also be a suspected stone meteorite. However, this test is only symbolic and does not mean that it is a meteorite. It can't be used as a basis to deny whether it is a meteorite, because not all rocks containing magnetism are meteorites, and it can't be blindly concluded that it is not a meteorite without magnetism. Because there are a lot of magnetic substances in various rocks of geochemical origin, magnetic minerals are not unique minerals in some types of meteorites, so they cannot be effectively classified by whether they contain magnetic substances or not. The most common magnetic minerals in various rocks in nature are iron-titanium, iron-manganese oxide, hydroxide, iron sulfide, iron, cobalt, nickel, alloy and so on. The magnetic state of these minerals belongs to antiferromagnetism (such as ilmenite, hematite, goethite, titanium spinel and meteorite pyrite). ) or ferrite (such as magnetite, maghemite, pyrrhotite and manganese spinel). ). Among them, ferrite magnetite and maghemite have the strongest magnetism. Some sedimentary rocks, igneous rocks and metamorphic rocks on the earth contain a lot of magnetic substances, which means that we can't blindly say that some rocks containing magnetism are meteorites when they are found in the wild.
Magnetic minerals are solid-liquid series magnetic substances formed at high temperature, and will also be desolventized at low temperature. In addition, magnetic minerals will be oxidized at various temperatures, which will have a certain impact on the combination and structure of magnetic minerals, and will also lead to uneven distribution of magnetic minerals in some rock masses. Some rocks or meteorites with uneven magnetic materials will have some large strength deviations due to different test locations or areas when conducting magnetic tests. Many people think that most meteorites contain iron minerals, and almost all types of meteorites can be attracted by magnets. This is a conceptual statistical data, because most iron meteorites are not easy to weather and are easy to be found, so they account for a large proportion of all kinds of meteorites that have been found. Of course, there are many kinds of magnetic-rich metal minerals and rocks of geochemical origin. For example, a large number of geochemical magnetite, hematite, goethite, manganese iron ore and limonite also have different magnetism, but they are not meteorite materials at all, but mostly geochemical metals and metal oxides. In some meteorites containing magnetic substances, or in various rocks with geochemical origin, there are a lot of magnetic substances, which shows that magnetic minerals have certain complexity and diversity in nature.
Some meteorites with no magnetic substance or weak magnetic substance are not easy to detect magnetism by some conventional means. If a simple test with a magnet shows that a meteorite is magnetic, it is not a meteorite without magnetism. This is a method of misjudgment and omission, and even some meteorites with weak magnetism or no magnetic substance will be discarded as garbage. Of course, judging only by magnetic test, some artificially cast metal lumps, alloy castings, blast furnace slag, etc. are often mistaken for meteorites. All kinds of rocks that obtain remanence under different physical and chemical conditions have different magnetic carriers. For example, the magnetic carriers of most igneous rocks are titanomagnetite and iron hematite, and pure iron and iron-nickel alloys are rare in nature, but the magnetism of some meteorites is related to iron and its alloys; The main magnetic carrier of deep-sea deposition is titanomagnetite; The problem of magnetic mineralogy of continental sedimentary rocks is extremely complicated, because these sediments are all deposited by fragments of primary igneous rocks, sedimentary rocks and metamorphic rocks. The latest research found that the main magnetic carrier of some continental and marine sediments may be bacterial magnetite. It has been found that some supermagnetic bacteria can even survive in an environment without air and oxygen. Therefore, magnetic minerals of biological origin may be more common than previously thought.
In addition, some magnetic minerals are formed by authigenic diagenesis, but fundamentally, most of the stable remanence obtained by various rocks comes from magnetic mineral particles carrying remanence. Therefore, ferrotitanium oxides in igneous rocks have always been the focus of magnetic mineralogy research. In addition, the chemical changes of magnetic minerals sometimes lead to obvious magnetic changes, that is, the so-called chemical change magnetic effect. Although this effect is sometimes not obvious, the phenomenon of re-magnetization of some rocks should be considered to be caused by chemical changes in nature. Whether it is all kinds of magnetic rocks originated from the earth or some meteorites rich in magnetic substances, the particle size, magnetic strength, shape and formation mode of magnetic minerals are also related to some extent, and they also have different genetic conditions and evolution experiences. We often hear people say that if a stone is magnetic, it will be said that it is a meteorite; if it is not magnetic, it will be arbitrarily said that it is not a meteorite. This is also an extremely wrong view. Because whether some meteorites contain or do not contain magnetic substances, or some rocks of earth origin contain or do not contain magnetic substances, there are different genetic and evolutionary conditions. Because of their genetic evolution and different rock types, they all have different lithofacies characteristics, structural characteristics, mineral assemblages, chemical properties and isotopic differences.
To sum up, that is to say, some stones are not necessarily meteorites if they are magnetic, and they cannot be said not to be meteorites without magnetism. Whether it is a meteorite or not, we can't blindly use magnetism to distinguish and characterize it. In ord to determine whether that suspect meteorite with or without magnetism is a real meteorite or a mineral or rock of earth origin,
First of all, we should understand the lithofacies, structure, mineral composition and chemical properties of various magnetic-rich, weak and non-magnetic meteorites. At the same time, we should also understand the lithofacies, structure, mineral composition, chemical properties and characteristics of various magnetic minerals on the earth. Only in this way can we distinguish them scientifically and effectively. However, in order to effectively identify and distinguish them, it is necessary to analyze and demonstrate the properties and characteristics of suspected meteorites, such as lithofacies, structure, mineral assemblage and chemical composition, with the help of various optical and electron microscopes, electron probes, X-ray diffraction and other professional instruments, which is the key to effectively distinguish and identify meteorites.