Iron is known since the dawn of humanity but never ever did people thought that it was sent down from the outer space simply because they found it in earthly rocks.

It is only in our modern time and particularly after the advancement in chemistry that man discovered that heavy metal including iron couldn't have been formed in the solar system even in the core of the sun where the temperature is so high(16 million Celsius) because such heavy metals including iron need It is now scientifically established that iron that was sent to the earth was formed in old stars after they reached its end-point.   

 How was iron formed?

  Iron is formed in stars five times more massive than the sun. In stars of the same size of the sun, hydrogen is fused into helium, when Hydrogen is used up, the star begins to expand. But in massive stars, nuclear fusion goes on and the temperature rises so high, this goes on till iron is formed; iron can't be fused, the star collapses explodes as a supernova where meteorites loaded with iron and other elements were sent down to the then ashes planets. Supernova core has a temperature of about 100 billion kelvins (100 GK); 6000 times the temperature of the sun's core. 

It is scientifically established that the earth was bombarded with iron meteorites and remain burning for millions of years. Because of the high density of iron, it found its way towards the core of the earth.

So iron wasn't formed in the earth, it was formed in the outer space in old stars.

What does the Holy Quran say about iron?

     God says in the Holy Quran what means

" We have already sent Our messengers with clear evidences and sent down with them the Scripture and the balance that the people may maintain [their affairs] in justice. And We sent down iron, wherein is great military might and benefits for the people, and so that Allah may make evident those who support Him and His messenger’s unseen. Indeed, Allah is Powerful and Exalted in Might. (57:25) 

In this verse God link between the holy books which were sent from heavens and the iron which was also, according to the verse, sent from heavens. The word" sent" implies moving a certain thing from a certain place to another place

God in His holy verse reminds us of His favours to us that He sent down iron, though there are many other elements He sent, the question is why God mentioned iron and not of other elements.
 

     The answer is given by a well-known microbiologist Michael Denton, in his book Nature’s Destiny, he says "Of all the metals there is none more essential to life than iron. It is the accumulation of iron in the center of a star which triggers a supernova explosion and the subsequent scattering of the vital atoms of life throughout the cosmos. It was the drawing by gravity of iron atoms to the center of the primeval earth that generated the heat which caused the initial chemical differentiation of the earth, the outgassing of the early atmosphere, and ultimately the formation of the hydrosphere. It is molten iron in the center of the earth which, acting like a gigantic dynamo, generates the earth’s magnetic field, which in turn creates the Van Allen radiation belts that shield the earth’s surface from destructive high-energy-penetrating cosmic radiation and preserve the crucial ozone layer from cosmic ray destruction…

     Without the iron atom, there would be no carbon-based life in the cosmos; no supernovae, no heating of the primitive earth, no atmosphere or hydrosphere. There would be no protective magnetic field, no Van Allen radiation belts, no ozone layer, no metal to make hemoglobin [in human blood], no metal to tame the reactivity of oxygen, and no oxidative metabolism.
 

     The intriguing and intimate relationship between life and iron, between the red color of blood and the dying of some distant star, not only indicates the relevance of metals to biology but also the biocentricity of the cosmos… "

A Numeric Miracle

     This is a remarkably some modern findings of science already mentioned in the Holy Quran. So many articles were written about this miracle and proves that The Holy Quran is revealed by God … there will be new discoveries in the horizon of many miracles will be found ...I think the features in the Holy Quran that remained unknown will give more significant meanings.
 

     The Holy Quran is like the fabric of the universe, every letters, every word and every Surah are in accordance to some numeric miracles. Scientists are now doing their best to find out more about the Holy Book. For example, there is a numeric miracle in the Holy Quran concerning iron.

     Surat al-Hadid 25, which refers to iron, contains two rather interesting mathematical codes. “Al- Hadid” is the 57th surah in the Qur’an. The abjad of the word “Al-Hadid” in Arabic, when the numerological values of its letters are added up, is also 57. The numerological value of the word “hadid” alone is 26. And 26 is the atomic number of iron.