The first scientific understanding of the origin of meteorites comes to us from Anaxagoras, a Greek philosopher and astronomer. He predicted in the 5th century BC by observing a comet the place where the latter will arrive on earth, thus giving an explanation about the origin of these stones.
This extra-terrestrial origin and the spectacular side of a meteorite which arrives in the atmosphere means that the people who have seen these celestial bodies arrive on earth have further nourished the myths and legends around meteorites.
Very often, meteorites were used as Betyle, that is to say a kind of sacred stone which could be the object of veneration and be considered as "divine dwellings", by possessing a Betyle, one holds a god in the palm of our hand. [Lenormant F., “Les betyles”, Revue de l’histoire des religions, vol. 3, t. 409, 1881]
It was also not uncommon for some of these meteorites to be the object of a cult and to take on great importance for a population, as evidenced by this coin which dates from the 3rd century, representing a meteorite in its temple.
Another aspect that has aroused men's admiration for the meteorite over the centuries is the fact that long before the Iron Age and therefore the mastery of this material by man (steelmaking) - the meteorite was the only source of iron available.
Indeed, the fact that iron is very sensitive to oxidation and corrosion means that it was very rare to find it in its native (non-oxidized) state in nature.
Obviously, the rarity of meteorites has always meant that the use of this meteorite iron was intended only for the production of very high value pieces, often reserved for the elite.
In Egypt we have found pearl necklaces dating from 3200 BC, whose beads are made of meteorite, but the most emblematic example is that of Tutankhamun's dagger, dating from the 14th century BC, and whose blade was made of meteoric iron.
It was natural that this material, considered a gift from the gods to men, should be used to make this dagger for the pharaoh, divine representative on earth. [Jacquet E., Meteorites and their secrets , Editions Ellipses, 2017]
But ultimately, what is a meteorite?
Strictly speaking, a meteorite is a body of extra-terrestrial origin which was not totally destroyed during its arrival in the Earth's atmosphere (very high temperatures) and its impact on Earth. It is considered that a meteorite loses between 99% and 99.9% of its original volume when it arrives on earth. [Bouley S. and Zanda B., Impact, from meteorites to craters, Belin, 2017.]
Meteorites can have different aspects depending on their compositions, there are 3 main categories: [Notkin's G., Meteorwritings - Meteorite types and classification , Geology.com, 2022]
Mixed meteorites (rocky and iron)
They represent the largest group of meteorites. They have an appearance that at first glance looks like an earthly rock.
If the fall of these meteorites is recent, these stones present a black crust which was formed by the heat created during the penetration into the Earth's atmosphere.
Despite their rocky nature, these stones often contain a sufficiently large proportion of iron for them to be ferromagnetic (attracted by a magnet).
Where these meteorites are interesting is that some of them called "Chondrites" may contain small inclusions called "Chondres" which are in the form of colored grains. These come from the solar nebula and are therefore older than the formation of our planet and the rest of the solar system. It is therefore one of the oldest materials that we can study on earth.
The majority of this type of meteorites are composed of 90 to 95% iron, the remaining 5 to 10% are mainly nickel and trace elements.
The iron-nickel alloys (mainly kamacite and taenite) present in these meteorites fit together geometrically and form a crystalline pattern called the "Wilmanstätten pattern", named after Alois von Beckh Widmanstätten who was the first to describe these motifs in the 19th century.
In order to observe these patterns, the surface of the meteorite must be prepared by cutting, polishing and metallographic development (often using nitric acid).
Mixed meteorites (rocky and iron):
These meteorites are even rarer than the last two and represent less than 2% of all meteorites discovered to date. Composed of approximately 50% of an iron-nickel alloy and minerals.
Some of these mixed meteorites called Pallasite are particularly interesting since they reveal translucent mineral zones (often olivine) which seem set in a complex metallic structure as shown in the photograph below:
The name Pallasite comes from the name of a German explorer who was the first to describe this type of meteorite in the 18th century.
Finally, one of the rarest meteorites is mesosiderite, composed of an iron-nickel alloy and silicates. Their appearance once cut and polished is very contrasting, with patterns formed of very shiny black and silver elements.
Of the thousands of meteorites listed to date, only less than a hundred have been identified as mesosiderites.
Thank you for your reading, I hope you enjoyed this article during which we were able to discover the very special bond that could be made.
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