In a corner that Hua Feng didn't know, an underground laboratory was sorting out the meteorite data, and everything seemed to be in order in such a confined space.

The largest preserved iron meteorite in the world is the Hoba iron meteorite in Namibia, Africa, weighing about 60 tons. This is followed by the Yokae 1 iron meteorite in Greenland, which weighs about 33 tons. China's Xinjiang iron meteorite, weighing about 28 tons, is the world's third largest iron meteorite. The world's largest stony meteorite is the Jilin meteorite, with a total weight of 2,550 kilograms, and the Jilin No. 1 meteorite, weighing 1,770 kilograms, is the largest stony meteorite mass that has been collected.

In addition, there is another type of meteorite called "glass meteorite". It is black or dark green in color, a bit like a stone, but not a stone. It's kind of like glass, but it's a very special glass-like substance that doesn't crystalline. It comes in a variety of shapes, is generally not large, and weighs from a few grams to dozens of grams. The identification of glass meteorites mainly depends on the place where the sample was found and its chemical isotope characteristics, and the chemical isotope characteristics are used as the final basis. So far, hundreds of thousands of suspected glass meteorites have been discovered, and it is strange that their distribution is clearly regional, and the cause of their regional occurrence has not yet been determined.

"Hanshu Du Ye Biography": "Ye Yanmin's false words and deeds, and Gu Yongyan's king bought private land, and the comet meteorite Mu Fei occupied it, and the language is in the "Five Elements Chronicles". ”

Wang Tao of the Qing Dynasty "Talking about the Urn and the Meteorite": "The meteorites and meteorites contained in the history of various countries are also this thing. ”

Meteorites burn and abrasive in the atmosphere, and their forms are round and angular.

Craters: The surface of meteorites is covered with craters of different sizes and depths, that is, melt craters. Many meteorites also have shallow, elongated gas marks, which may be left by the shedding of minerals with low melting points.

Molten crust: When a meteorite passes through the atmosphere, the extremely high temperature causes the surface of the meteorite to melt, creating a vitreous layer in the micron to millimeter range, which is called molten crust. When a meteorite exists on the surface for a long time, its molten shell is easily weathered and disappears.

Specific gravity: Meteorites have a large specific gravity of iron and nickel, and the specific gravity of iron meteorites can reach 8, and stone meteorites often contain 20 iron and nickel, which is larger than the specific gravity of ordinary rocks. However, there are a very small number of stony meteorites (such as carbonaceous chondrites) that contain no or very low metal content, and their density is similar to that of ordinary earth rocks.

Magnetism: Various meteorites have magnetic properties of varying intensity due to the presence of iron. Weathered meteorites are not magnetic, so they are not considered meteorites.

Streaks: Meteorites rubbed against unglazed porcelain plates generally have no streaks or only light gray streaks, while iron ore streaks are black or brownish-red, which is distinguished.

Through the observation of some meteorites embedded with gravel, people understand that the space environment when small celestial bodies evolve in space is: there are a large number of small celestial bodies orbiting the sun, and the diameter of these small celestial bodies is as large as tens of kilometers, hundreds of kilometers, as small as tens of centimeters, several centimeters, and even smaller than the size of pebbles and dust particles. Small celestial bodies often collide with each other during their orbit, and generally speaking, small celestial bodies with a scale of more than 10 centimeters are hit by thousands, tens of thousands of gravel or dust particles.

Since these small celestial bodies are moving in space at cosmic speed, they are much faster than the travel speed of guns and shells. Therefore, the impact force generated by the collision between small celestial bodies against each other is very large. Under the action of this impact force, high temperature and high pressure will be generated on the impact surface between small celestial bodies, and the mineral rock will be melted and metamorphosed to form a molten body. The shape of this melt comes in a variety of shapes. In a nutshell, the metamorphic molten body left on the surface of a small body is the crust, crater, and trough of a small body. The metamorphic melt left inside the small celestial body is the wall of the lava cave and the melt belt. Observations of meteorites have shown that the thickness of the molten crust created by each impact is generally between one millimeter and ten millimeters.

When a small object is hit by thousands of gravel or dust particles, a large number of small local melts are superimposed to form the outer shell of the small body. Generally speaking, the greater the impact force, the greater the melt produced, and the thicker the outer shell of the small celestial body built. Usually the shells of the small objects we see on meteorites are a few millimeters or more centimeters thick. Take a look at the large meteorite in Xinjiang, the thick shell was built by the impact of thousands of gravel and sand particles.

Collisions between small celestial bodies often change the structure and structure of their interiors. For example, chondrites can be changed to nochondrites, and of course, nodulares can be transformed into chondrites. A small celestial body falling to the ground is a meteorite. When it passes through the earth's atmosphere, it produces strong friction with the air, and under the action of high pressure and high temperature, its appearance will often melt and deteriorate, and after cooling, a layer of molten crust with a thickness of about one millimeter will be born on the surface of the meteorite.

Generally speaking, there are two kinds of molten crusts of the same meteorite, one is the molten crust produced by the collision between asteroids in space, and the other is the molten crust produced by entering the Earth's atmosphere and rubbing against the air.

When meteorites fly at high altitudes, the surface temperature reaches several thousand degrees. At such high temperatures, the surface of the meteorite melts into liquid. Later, due to the blockage of the dense atmosphere in the lower layers, his speed became slower and slower, and the molten surface cooled down, forming a thin crust called "molten crust". The molten shell is very thin, generally around 1 mm, and the color is black or brown. In the process of cooling the molten shell, the traces of air flowing on the surface of the meteorite are also retained, which are called "gas marks".

The air mark looks a lot like a finger print pressed on the dough. Molten crusts and air marks are the main features of the surface of meteorites. If you see a rock or iron with such a molten shell or air mark on its surface, you can immediately conclude that it is a meteorite. However, some meteorites that fall older are due to long-term wind, sun and rain, and the molten shell has fallen off, and the air mark is not easy to identify, but that doesn't matter, there are other ways to identify it.

A stony meteorite looks a lot like a rock on Earth, and if you weigh it by hand, you will feel that it is heavier than a rock of the same volume. Stone meteorites generally contain a few percent of iron, which is magnetic, and you will feel it when you try it with a magnetite. In addition, if you look closely at the cross-section of the stony meteorite, you will find that there are quite a few small chondrites.

Pellets are generally about 1 mm, and some are larger than 2~3 mm. More than 90% of stony meteorites have such chondrites, which are produced when meteorites are generated. It is an important marker for identifying stony meteorites. The main components of iron meteorites are iron and nickel. Among them, iron accounts for about 90%, and the nickel content is generally between 4~8%, and the nickel content in the earth's natural iron is generally not so much.

A section is cut on an iron meteorite, polished, and eroded with 5% nitric acid alcohol, and the shiny end face will show special stripes, like a lattice. This is because the iron meteorite itself is unevenly distributed, some places contain more nickel, some places have less, the part with more nickel content is chemically stable, not easy to be corroded by acid, and the part with less nickel content is corroded by acid and becomes rough and dull, so that these bright and dark parts form a lattice-like stripe.

These streaks occur with the exception of a very small number of meteorites with a very high nickel content. This is one of the main methods of identifying iron meteorites. Stony-iron meteorites are extremely rare and are composed of stone and iron, and it contains roughly equal iron and silicate minerals.

Among the three types of meteorites, the most stony meteorites, on March 8, 1976, a large-scale meteorite rain landed in Jilin District, Jilin Province, China, which was a stony chondrite meteorite shower. The meteorite rain scattered an area of 4 to 500 square kilometers, and more than 100 meteorites were collected, with a total weight of more than 2,600 kilograms. Among them, the largest ** meteorite weighs 1770 kilograms, which is the heaviest stone meteorite found in the world. In second place is the American Nortonite meteorite, which weighs 1079 kilograms. Iron meteorites are much heavier than stony meteorites, and the heaviest piece is in Namibia, Africa, with the name Goba meteorite, which weighs 60 tons. A large piece of meteorite in Xinjiang, China, weighs 30 tons, which is the third largest in the world.

Most meteoroids disintegrate when they enter the atmosphere, and it is estimated that there are still about 500 meteorites per year, ranging from marbles to basketballs, to the ground, but usually only 5 to 10 meteors are found to fall each year and are known and recovered by scientists. A few meteorites are large enough to create huge impact craters, while others are not large enough to reach terminal velocity when they hit the ground, creating at most a small crater.

Large meteorites may still be close to their second cosmic velocity when they hit the ground, leaving a crater behind by a super-high-velocity impact. The type of crater depends on the size of the meteorite, its composition, the degree of fragmentation, and the angle of impact it enters. The force of this collision has the potential to cause widespread damage. The most common hypervelocity impacts on Earth are caused by iron meteorites, which are the easiest to pass through the atmosphere.

Examples of impact craters caused by iron meteorites include Barringer Crater, Odessa Crater, Waba Crater, and Wolf Creek Crater, where associated iron meteorites have been found.

In contrast, large enough stony meteoroids or snow globes or asteroids like comets, even if they weigh millions of metric tons, can still be destroyed as they enter and pass through the atmosphere without leaving impact craters. While such disintegration events are rare, they cause alarming oscillations, which may be the case with the famous Tunguska event.

Very large stony meteoroids, hundreds of meters in diameter or larger, with masses of tens of millions of metric tons or more, can fall to the Earth's surface and strike large impact craters, but this is very rare.

Such impacts are usually surrounded by enormous amounts of energy, so the impact is completely destroyed without the meteorite being left behind.