The Iron Ring Ceremony being upon us again, this OTSOG column will cover a man who made his name in mineralogy. His discoveries on how crystals worked would later allow us to develop theories about crystal structures, dislocations, and slip, letting us predict the ductility of metals and find appropriate alloying elements.
René Just Haüy (1743-1822) was born in the village of St.-Just-en-Chaussée, France, to a family of weavers. In pre-revolutionary France, working class people didn’t have a lot of opportunities to advance in society. But luckily for René, as a kid he was very musical, which attracted the attention of a local monk and allowed him to receive an education at the monastery. He impressed his teachers, to the point where he was awarded a scholarship to the University of Paris. Even then, he didn’t have enough money to pay his student fees, so just as students today look to co-op for their income, Haüy had to interrupt his studies, spending some time playing violin and singing in a choir to make ends meet. But he did graduate and earned “arts” (which, at the time, included the natural sciences) and theology degrees. In 1770, he received ordination as a Catholic priest, and a teaching post at the University of Paris.
Haüy was originally asked to teach Latin courses. But he had his own hobbies too – one area of interest was botany, and he spent a lot of time in a garden at the university, cataloguing the different types of flowers which grew there. He was impressed with the regularity with which flowers grew petals; for example, roses always have exactly five petals. He soon became friends with Louis Daubenton, who studied minerals. At first, he was disappointed that crystals seemed to follow no regular pattern – calcite crystals, for example, came in many different shapes, some that did not resemble any regular geometric solid.
Supposedly, one fateful day, at the home of a fellow professor, his colleague handed him a piece of calcite … but he dropped it. While cleaning up the pieces, he noticed suddenly that all of the pieces had rhombohedral shapes. What were the chances of that? Although it is a nice story, it could just as easily be a legend like Newton’s apple falling on his head. More likely, Haüy simply heard about the research of the Swedish chemists Torbern Bergman and Johan Gahn, who had hypothesized that all calcite crystals were made up of rhombohedrons a few years earlier.
Haüy started acquiring samples of minerals for an experiment. He gathered a few calcite crystals of various shapes, and smashed a hammer into each one. He discovered that no matter what the original shape of the crystal, when broken up into pieces they were always rhombohedrons. When he tried the experiment with pyrite, all the pieces were cubes. When he smashed barite, all the pieces were rectangular prisms. He came to the conclusion that all minerals only have one basic crystal structure, and all the other crystal shapes which are observed are simply combinations of the basic building block superimposed on each other at various angles.
Haüy further discovered that the length, width, and height of the building blocks, the basic crystal or lattice structures, could always be expressed as rational number multiples of each other (1:1, 3:2, 2:1, etc). This became known as Haüy’s Law of Rational Intercepts.
When his discoveries were published, Haüy was named to the Académie des Sciences. But he soon ran into political difficulties. In 1792, the King and Queen of France were removed from power by revolution. As the Catholic Church had ties to the old regime, Father Haüy was arrested as a suspected counter-revolutionary. He took his jail time in stride – after all, he was already used to being stuck in his room alone doing research. After fellow scientists offered pleas on his behalf to the new regime, he was released and given his tenure back. He was also named to a committee to establish a new system of units, which would eventually become the SI system we all know and love. By the time of his death, Haüy’s books had become the standard text for materials science in France.
Like many other brilliant scientists, Haüy had an unfortunate tendency not to give his predecessors their due, and was reluctant to admit his own mistakes. But he definitely went beyond Bergman and Gahn, generalizing their research to arrive at a universal law of crystallography, and he did pave the way for later researchers. In the nineteenth century, William Miller proposed vector symbols like (111) for lattice planes; based on Haüy’s discovery that the ratio between the dimensions of a crystal would be a rational number ratio, all lattice planes could be symbolized with three numbers. The modern classification of crystal systems (e.g. diamond cubic, hexagonal close-packed) is ultimately based on the work of Haüy.
Recent discoveries have called into question whether Haüy’s theories are really universal. In 2011, Dan Shechtman was awarded the Nobel Prize in Chemistry, for showing that structures could have order without being periodic repetitions of the same basic building block. These he labelled “quasicrystals”, because they cannot be broken down into a single crystal structure. But this just shows us how science works: as new research happens, older theories sometimes are found wanting. But this is no knock on Haüy – he has simply become one of the giants that today’s researchers are standing on.
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