The Qur'an contains many clear statements that mankind was made from clay. These can be found in Qur'an 3:49 (a bird is made by clay by the power of God), 6:2, 7:12, 15:26, 17:61, 38:71,76. But that's not the whole story. In Qur'an 15:26 there are some strange additions; mankind was made in clay "that gives forth sound, of black mud fashioned in shape", or from a different translation, "from dry clay and black moulded loam" (Dawood). Clearly, this is not the wet Monmorillonite clay that may have played an important part in the history of the earth in helping in the formation of the first organic molecules. Unfortunately this "scientifically" correct statement in the Qur'an falls foul of technicalities: the role clay played in the ancient evolution of life was merely that of a catalyst, and life does not come "from" clay at all. And... the formation of life from organic chemicals involved so many steps over such a period of time, that almost any statement about creating life "from" something could be said to be true.
Coincidentally some of our most ancient religions and philosophies have held that mankind was 'made' from clay. Although there some serious caveats to mention before the poor reader starts going all medieval: (1) they do not mean the precise substance as described by science, (2) life doesn't come "from" clay, some types of clay merely acted as a catalyst, and (3) we merely translate (quite a few) ancient words as 'clay' which were themselves used to describe a variety of materials. Nonetheless it is still nice that by luck some pre-science beliefs do actually hit on correct-sounding statements, even if for the wrong reasons. Finally, the use of clay as a building material of the gods makes sense in terms of human experience because after all, clay is what us Humans created models and figurines out of.
5000 years ago in Sumeria: It was said that the god Enki created humans by forming their shape in clay by laying in it1 and the goddess Aruru created the wild man Enkidu "from a piece of clay moistened with her own spittle"2. The Epic of Atrahasis records that humans are made from a mixture of clay and divine blood and saliva for the purpose of working the soil on the Earth (pictured on the right, from the British Museum).3
Greek science, 2500 years ago: Anaximander of Miletus (~610BCE-546BCE) was an early scientist from Ionia in ancient Greece. "He proposed the spontaneous origin of life in mud, the first animals being fish covered with spines. Some descendants of these fishes eventually abandoned the water and moved to dry land, where they evolved into other animals"4. A pleasing precursor to the theory of evolution!
The Hebrew Scriptures, 6th centuryBCE: "The LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul. [...] Out of the ground the LORD God formed every beast of the field, and every fowl of the air" (Genesis 2:7,19).
The pagan Stoics, from the 3rd centuryBCE, believed that "a human being is partly fire, partly made of lower clay; in so far as he is fire [...], he is part of God"5. Our earthly component came from clay.
When the authors of the Qur'an spoke of mankind being made of clay there were simply repeating a common cultural guess which although close to an element of truth, was in its detail incorrect. Furthermore those verses in the Qur'an that say we are created from clay, actually contradict others. Qur'an 23:14 and 96:1-2 say that mankind is created from a clot of blood; and has bones form before flesh (when in reality, flesh comes first during foetal development). None of that is correct or in the correct order. Many verses such as 16:4, 36:77, 76:2 and 80:19 say instead that mankind is created from a "small seed", or a "drop of seed", or a drop of 'mingled' or 'mixed' drops of sexual discharge. These statements are untrue in detail and, of course, completely forget the female egg. The Qur'an also announces, rather strangely, a verse which few have ever convincingly made sense of:
“So let man see from what he is created! He is created from a water gushing forth, proceeding from between the backbone and the ribs.”